<PAGE>

     As filed with the Securities and Exchange Commission on February 17, 2000.

                                                    Registration No. 333-_______

================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                             ----------------------

                                    FORM S-8
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                             ----------------------

                                  IBASIS, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                    DELAWARE
         (STATE OR OTHER JURISDICTION OF INCORPORATION OR ORGANIZATION)

                                   04-3332534
                      (I.R.S. EMPLOYER IDENTIFICATION NO.)

20 SECOND AVENUE, BURLINGTON, MASSACHUSETTS                             01803
  (Address of Principal Executive Offices)                            (Zip Code)

                             ----------------------

                            1997 STOCK INCENTIVE PLAN
                        1999 EMPLOYEE STOCK PURCHASE PLAN
                            (FULL TITLE OF THE PLAN)

                             ----------------------

                                   OFER GNEEZY
                                    President
                           and Chief Executive Officer
                                  iBasis, Inc.
                                20 Second Avenue
                              Burlington, MA 01803
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)

                                 (781) 505-7500
           TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE

                             ----------------------

                                    Copy to:
                              DAVID L. ENGEL, ESQ.
                             JOHAN V. BRIGHAM, ESQ.
                                BINGHAM DANA LLP
                               150 Federal Street
                           Boston, Massachusetts 02110
                                 (617) 951-8000

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>

------------------------------------- -------------------- --------------- ------------------- -------------------
------------------------------------- -------------------- --------------- ------------------- -------------------
                                                              Proposed          Proposed
              Title Of                                        Maximum           Maximum
             Securities                     Amount            Offering         Aggregate           Amount Of
               To Be                         To Be           Price Per          Offering          Registration
             Registered                   Registered         Share (1)           Price                Fee
------------------------------------- -------------------- --------------- ------------------- -------------------
<S>                                   <C>                  <C>             <C>                 <C>

Common Stock,
$0.001 par value per share                 6,200,000           $68.53          $424,886,000          $112,170
------------------------------------- -------------------- --------------- ------------------- -------------------
------------------------------------- -------------------- --------------- ------------------- -------------------

</TABLE>

(1) Estimated solely for the purpose of computing the registration fee pursuant
to Rule 457(h) under the Securities Act of 1933, as amended, based on the
average of the high and low prices of the Registrant's Common Stock, $0.001 par
value per share, reported by the Nasdaq National Market on February 15, 2000.


<PAGE>

                                      -2-

                                     PART II

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by iBasis, Inc. (the "REGISTRANT") with
the Securities and Exchange Commission (the "SEC") are hereby incorporated by
reference into this Registration Statement: (1) the Registrant's prospectus
filed pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended
(the "SECURITIES ACT"); (2) all other reports filed by the Registrant pursuant
to Sections 13(a) or 15(d) of the Exchange Act since December 31, 1998; and (3)
the description of the common stock of the Registrant, $0.001 par value per
share (the "COMMON STOCK"), contained in the Registrant's registration statement
on Form 8-A filed with the SEC on August 24, 1999 pursuant to Section 12(g) of
the Securities Exchange Act of 1934, as amended (the "EXCHANGE ACT"), including
any amendment or report filed for the purpose of updating such description.

         In addition, all documents filed pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Exchange Act subsequent to the date of this Registration
Statement and prior to the filing of a post-effective amendment which indicates
that all securities registered hereby have been sold or which deregisters all of
such securities then remaining unsold shall be incorporated by reference into
this Registration Statement as of the filing date of each.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145 of the Delaware General Corporation law empowers a Delaware
corporation to indemnify its officers and directors and certain other persons to
the extent and under the circumstances set forth therein.

         The form of the Amended and Restated Certificate of Incorporation of
the Registrant and the Amended and Restated By-Laws of the Registrant, as
amended to date, provide for indemnification of officers and directors of the
Registrant and certain other persons against liabilities and expenses incurred
by any of them in certain stated proceedings and under certain stated
conditions.

         The Registrant may maintain insurance for the benefit of its directors,
officers, employees, agents and certain other persons, insuring such persons
against any expense, liability, or loss, including liability under the
securities laws.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

<PAGE>

                                      -3-

         The following exhibits are filed as part of this Registration
Statement:

EXHIBIT NO.                                 DESCRIPTION OF DOCUMENTS

         4.1      Amended and Restated  Certificate of  Incorporation  of the
                  Registrant,  incorporated  by reference to Exhibit No. 3.1 to
                  the  Registrant's Registration Statement on Form S-1
                  (file No. 333-85545), filed on November 9, 1999.

         4.2.     Amended and Restated  By-Laws of the Registrant,  incorporated
                  by reference to Exhibit No. 3.2 to the Registrant's
                  Registration  Statement on Form S-1 (No. 333-85545).

         4.3      1997 Stock  Incentive  Plan,  incorporated  by reference to
                  Exhibit No. 10.8 to the  Registrant's  Registration  Statement
                  on Form S-1 (No. 333-85545).

         4.4      1999 Employee Stock Purchase Plan, as amended, incorporated
                  by reference to Exhibit No. 10.26 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-96533), filed
                  February 10, 2000.

         5        Opinion of Bingham Dana LLP as to the legality of the
                  securities being registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of Bingham Dana LLP (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this
                  Registration Statement).

ITEM 9.  UNDERTAKINGS

         (A) The undersigned registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
                           are being made, a post-effective amendment to this
                           registration statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the registration statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the registration
                                    statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not exceed
                                    that which was registered) and any deviation
                                    from the low or high and of the estimated
                                    maximum offering range may be reflected in
                                    the form of prospectus filed with the
                                    Commission pursuant to Rule 424(b) if, in
                                    the aggregate, the changes in volume and
                                    price represent no more than 20 percent
                                    change in the maximum aggregate offering
                                    price set forth in the "Calculation of
                                    Registration Fee" table in the effective
                                    registration statement.

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the registration
                                    statement or any material change to such
                                    information in the registration statement;

<PAGE>

                                       -4-

                           PROVIDED, HOWEVER, that paragraphs (1)(i) and (1)(ii)
                           do not apply if the information required to be
                           included in a post-effective amendment by those
                           paragraphs is contained in periodic reports filed
                           with or furnished to the Commission by the registrant
                           pursuant to Section 13 or Section 15(d) of the
                           Securities Exchange Act of 1934, as amended (the
                           "Exchange Act") that are incorporated by reference in
                           the registration statement.

                  (2)      That, for the purpose of determining any liability
                           under the Securities Act, each such post-effective
                           amendment shall be deemed to be a new registration
                           statement relating to the securities offered therein,
                           and the offering of such securities at that time
                           shall be deemed to be the initial BONA FIDE offering
                           thereof.

                  (3)      To remove from registration by means of a
                           post-effective amendment any of the securities being
                           registered which remain unsold at the termination of
                           the offering.

         (B)      The undersigned registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  each filing of the registrant's annual report pursuant to
                  Section 13(a) or Section 15(d) of the Exchange Act (and, where
                  applicable, each filing of an employee benefit plan's annual
                  report pursuant to Section 15(d) of the Exchange Act) that is
                  incorporated by reference in the registration statement shall
                  be deemed to be a new registration statement relating to the
                  securities offered therein, and the offering of such
                  securities at that time shall be deemed to be the initial BONA
                  FIDE offering thereof.

         (C)      Insofar as indemnification for liabilities arising under the
                  Securities Act may be permitted to directors, officers and
                  controlling persons of the registrant pursuant to the
                  foregoing provisions, or otherwise, the registrant has been
                  advised that in the opinion of the Securities and Exchange
                  Commission such indemnification is against public policy as
                  expressed in the Securities Act and is, therefore,
                  unenforceable. In the event that a claim for indemnification
                  against such liabilities (other than the payment by the
                  registrant of expenses incurred or paid by a director, officer
                  or controlling person of the registrant in the successful
                  defense of any action, suit or proceeding) is asserted by such
                  director, officer or controlling person in connection with the
                  securities being registered, the registrant will, unless in
                  the opinion of its counsel the matter has been settled by
                  controlling precedent, submit to a court of appropriate
                  jurisdiction the question whether such indemnification by it
                  is against public policy as expressed in the Securities Act
                  and will be governed by the final adjudication of such issue.


<PAGE>

                                      -5-

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the Town of Burlington, Commonwealth of Massachusetts, as of
the 16th day of February 2000.

                                                 iBASIS, INC.

                                                 By: /S/ OFER GNEEZY
                                                    -----------------
                                                     Ofer Gneezy
                                                     President and Chief
                                                     Executive Officer


<PAGE>

                                      -6-

                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoints Ofer Gneezy,
Michael Hughes, and each of them severally, his true and lawful attorney-in-fact
with the authority to execute in the name of each such person, and to file with
the Securities and Exchange Commission, together with any exhibits thereto and
other documents therewith, any and all amendments (including without limitation
post-effective amendments) to this Registration Statement on Form S-8 necessary
or advisable to enable the Registrant to comply with the Securities Act of 1933,
as amended, and any rules, regulations, and requirements of the Securities and
Exchange Commission in respect thereof, which amendments may make such other
changes in the Registration Statement as the aforesaid attorney-in-fact
executing the same deems appropriate.

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities indicated as of the 16th day of February 2000.


         SIGNATURE                                            TITLE

/S/ OFER GNEEZY                          President, Chief Executive Officer and
---------------------                    Director (Principal Executive Officer)
Ofer Gneezy

/S/ GORDON VANDERBRUG                    Executive Vice President and Director
---------------------
Gordon J. VanderBrug

/S/ MICHAEL J. HUGHES                    Vice President, Finance and Chief
---------------------                    Financial Officer (Principal Financial
Michael Hughes                           and Accounting Officer)

/S/ ROBERT MAGINN                        Director
---------------------
Robert Maginn

                                         Director
---------------------
Charles S. Houser

/S/ IZHAR ARMONY                         Director
---------------------
Izhar Armony

/S/ JOHN JARVE                           Director
---------------------
John Jarve

/S/ CHARLES N. CORFIELD                  Director
---------------------
Charles N. Corfield

/S/ CHARLES M. SKIBO                     Director
---------------------
Charles M. Skibo

                                         Director
---------------------
Carl Redfield


<PAGE>

                                      -7-


                                  EXHIBIT INDEX

EXHIBIT NO.                                 DESCRIPTION OF DOCUMENTS

         4.1      Amended and Restated Certificate of Incorporation of the
                  Registrant, incorporated by reference to Exhibit No. 3.1 to
                  the Registrant's Registration Statement on Form S-1 (file No.
                  333-85545), filed on November 9, 1999.

         4.2.     Amended and Restated By-Laws of the Registrant, incorporated
                  by reference to Exhibit No. 3.2 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-85545).

         4.3      1997 Stock Incentive Plan, incorporated by reference to
                  Exhibit No. 10.8 to the Registrant's Registration Statement on
                  Form S-1 (No. 333-85545).

         4.4      1999 Employee Stock Purchase Plan, as amended, incorporated
                  by reference to Exhibit No. 10.26 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-96533), filed
                  February 10, 2000.

         5        Opinion of Bingham Dana LLP as to the legality of the
                  securities being registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of Bingham Dana LLP (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this
                  Registration Statement).
[{"type": "S-8", "sequence": "1", "description": "S-8", "secsgml_size_bytes": 19303}]
{"company-data": {"conformed-name": "IBASIS INC", "cik": "0001091756", "assigned-sic": "7389", "irs-number": "043332534", "state-of-incorporation": "DE"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-30642", "film-number": "548665"}, "business-address": {"street1": "20 SECOND AVE", "city": "BURLINGTON", "state": "MA", "zip": "01803", "phone": "7815057500"}, "mail-address": {"street1": "20 SECOND AVE", "city": "BURLINGTON", "state": "MA", "zip": "01803"}}
As filed with the Securities and Exchange Commission on February 17, 2000.

                                                    Registration No. 333-_______

================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                             ----------------------

                                    FORM S-8
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                             ----------------------

                                  IBASIS, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                    DELAWARE
         (STATE OR OTHER JURISDICTION OF INCORPORATION OR ORGANIZATION)

                                   04-3332534
                      (I.R.S. EMPLOYER IDENTIFICATION NO.)

20 SECOND AVENUE, BURLINGTON, MASSACHUSETTS                             01803
  (Address of Principal Executive Offices)                            (Zip Code)

                             ----------------------

                            1997 STOCK INCENTIVE PLAN
                        1999 EMPLOYEE STOCK PURCHASE PLAN
                            (FULL TITLE OF THE PLAN)

                             ----------------------

                                   OFER GNEEZY
                                    President
                           and Chief Executive Officer
                                  iBasis, Inc.
                                20 Second Avenue
                              Burlington, MA 01803
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)

                                 (781) 505-7500
           TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE

                             ----------------------

                                    Copy to:
                              DAVID L. ENGEL, ESQ.
                             JOHAN V. BRIGHAM, ESQ.
                                BINGHAM DANA LLP
                               150 Federal Street
                           Boston, Massachusetts 02110
                                 (617) 951-8000

                         CALCULATION OF REGISTRATION FEE
------------------------------------- -------------------- --------------- ------------------- -------------------
------------------------------------- -------------------- --------------- ------------------- -------------------
                                                              Proposed          Proposed
              Title Of                                        Maximum           Maximum
             Securities                     Amount            Offering         Aggregate           Amount Of
               To Be                         To Be           Price Per          Offering          Registration
             Registered                   Registered         Share (1)           Price                Fee
------------------------------------- -------------------- --------------- ------------------- -------------------
Common Stock,
$0.001 par value per share                 6,200,000           $68.53          $424,886,000          $112,170
------------------------------------- -------------------- --------------- ------------------- -------------------
------------------------------------- -------------------- --------------- ------------------- -------------------
(1) Estimated solely for the purpose of computing the registration fee pursuant
to Rule 457(h) under the Securities Act of 1933, as amended, based on the
average of the high and low prices of the Registrant's Common Stock, $0.001 par
value per share, reported by the Nasdaq National Market on February 15, 2000.
-2-

                                     PART II

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by iBasis, Inc. (the "REGISTRANT") with
the Securities and Exchange Commission (the "SEC") are hereby incorporated by
reference into this Registration Statement: (1) the Registrant's prospectus
filed pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended
(the "SECURITIES ACT"); (2) all other reports filed by the Registrant pursuant
to Sections 13(a) or 15(d) of the Exchange Act since December 31, 1998; and (3)
the description of the common stock of the Registrant, $0.001 par value per
share (the "COMMON STOCK"), contained in the Registrant's registration statement
on Form 8-A filed with the SEC on August 24, 1999 pursuant to Section 12(g) of
the Securities Exchange Act of 1934, as amended (the "EXCHANGE ACT"), including
any amendment or report filed for the purpose of updating such description.

         In addition, all documents filed pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Exchange Act subsequent to the date of this Registration
Statement and prior to the filing of a post-effective amendment which indicates
that all securities registered hereby have been sold or which deregisters all of
such securities then remaining unsold shall be incorporated by reference into
this Registration Statement as of the filing date of each.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145 of the Delaware General Corporation law empowers a Delaware
corporation to indemnify its officers and directors and certain other persons to
the extent and under the circumstances set forth therein.

         The form of the Amended and Restated Certificate of Incorporation of
the Registrant and the Amended and Restated By-Laws of the Registrant, as
amended to date, provide for indemnification of officers and directors of the
Registrant and certain other persons against liabilities and expenses incurred
by any of them in certain stated proceedings and under certain stated
conditions.

         The Registrant may maintain insurance for the benefit of its directors,
officers, employees, agents and certain other persons, insuring such persons
against any expense, liability, or loss, including liability under the
securities laws.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.
-3-

         The following exhibits are filed as part of this Registration
Statement:

EXHIBIT NO.                                 DESCRIPTION OF DOCUMENTS

         4.1      Amended and Restated  Certificate of  Incorporation  of the
                  Registrant,  incorporated  by reference to Exhibit No. 3.1 to
                  the  Registrant's Registration Statement on Form S-1
                  (file No. 333-85545), filed on November 9, 1999.

         4.2.     Amended and Restated  By-Laws of the Registrant,  incorporated
                  by reference to Exhibit No. 3.2 to the Registrant's
                  Registration  Statement on Form S-1 (No. 333-85545).

         4.3      1997 Stock  Incentive  Plan,  incorporated  by reference to
                  Exhibit No. 10.8 to the  Registrant's  Registration  Statement
                  on Form S-1 (No. 333-85545).

         4.4      1999 Employee Stock Purchase Plan, as amended, incorporated
                  by reference to Exhibit No. 10.26 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-96533), filed
                  February 10, 2000.

         5        Opinion of Bingham Dana LLP as to the legality of the
                  securities being registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of Bingham Dana LLP (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this
                  Registration Statement).

ITEM 9.  UNDERTAKINGS

         (A) The undersigned registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
                           are being made, a post-effective amendment to this
                           registration statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the registration statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the registration
                                    statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not exceed
                                    that which was registered) and any deviation
                                    from the low or high and of the estimated
                                    maximum offering range may be reflected in
                                    the form of prospectus filed with the
                                    Commission pursuant to Rule 424(b) if, in
                                    the aggregate, the changes in volume and
                                    price represent no more than 20 percent
                                    change in the maximum aggregate offering
                                    price set forth in the "Calculation of
                                    Registration Fee" table in the effective
                                    registration statement.

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the registration
                                    statement or any material change to such
                                    information in the registration statement;
-4-

                           PROVIDED, HOWEVER, that paragraphs (1)(i) and (1)(ii)
                           do not apply if the information required to be
                           included in a post-effective amendment by those
                           paragraphs is contained in periodic reports filed
                           with or furnished to the Commission by the registrant
                           pursuant to Section 13 or Section 15(d) of the
                           Securities Exchange Act of 1934, as amended (the
                           "Exchange Act") that are incorporated by reference in
                           the registration statement.

                  (2)      That, for the purpose of determining any liability
                           under the Securities Act, each such post-effective
                           amendment shall be deemed to be a new registration
                           statement relating to the securities offered therein,
                           and the offering of such securities at that time
                           shall be deemed to be the initial BONA FIDE offering
                           thereof.

                  (3)      To remove from registration by means of a
                           post-effective amendment any of the securities being
                           registered which remain unsold at the termination of
                           the offering.

         (B)      The undersigned registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  each filing of the registrant's annual report pursuant to
                  Section 13(a) or Section 15(d) of the Exchange Act (and, where
                  applicable, each filing of an employee benefit plan's annual
                  report pursuant to Section 15(d) of the Exchange Act) that is
                  incorporated by reference in the registration statement shall
                  be deemed to be a new registration statement relating to the
                  securities offered therein, and the offering of such
                  securities at that time shall be deemed to be the initial BONA
                  FIDE offering thereof.

         (C)      Insofar as indemnification for liabilities arising under the
                  Securities Act may be permitted to directors, officers and
                  controlling persons of the registrant pursuant to the
                  foregoing provisions, or otherwise, the registrant has been
                  advised that in the opinion of the Securities and Exchange
                  Commission such indemnification is against public policy as
                  expressed in the Securities Act and is, therefore,
                  unenforceable. In the event that a claim for indemnification
                  against such liabilities (other than the payment by the
                  registrant of expenses incurred or paid by a director, officer
                  or controlling person of the registrant in the successful
                  defense of any action, suit or proceeding) is asserted by such
                  director, officer or controlling person in connection with the
                  securities being registered, the registrant will, unless in
                  the opinion of its counsel the matter has been settled by
                  controlling precedent, submit to a court of appropriate
                  jurisdiction the question whether such indemnification by it
                  is against public policy as expressed in the Securities Act
                  and will be governed by the final adjudication of such issue.
-5-

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the Town of Burlington, Commonwealth of Massachusetts, as of
the 16th day of February 2000.

                                                 iBASIS, INC.

                                                 By: /S/ OFER GNEEZY
                                                    -----------------
                                                     Ofer Gneezy
                                                     President and Chief
                                                     Executive Officer
-6-

                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoints Ofer Gneezy,
Michael Hughes, and each of them severally, his true and lawful attorney-in-fact
with the authority to execute in the name of each such person, and to file with
the Securities and Exchange Commission, together with any exhibits thereto and
other documents therewith, any and all amendments (including without limitation
post-effective amendments) to this Registration Statement on Form S-8 necessary
or advisable to enable the Registrant to comply with the Securities Act of 1933,
as amended, and any rules, regulations, and requirements of the Securities and
Exchange Commission in respect thereof, which amendments may make such other
changes in the Registration Statement as the aforesaid attorney-in-fact
executing the same deems appropriate.

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities indicated as of the 16th day of February 2000.

         SIGNATURE                                            TITLE

/S/ OFER GNEEZY                          President, Chief Executive Officer and
---------------------                    Director (Principal Executive Officer)
Ofer Gneezy

/S/ GORDON VANDERBRUG                    Executive Vice President and Director
---------------------
Gordon J. VanderBrug

/S/ MICHAEL J. HUGHES                    Vice President, Finance and Chief
---------------------                    Financial Officer (Principal Financial
Michael Hughes                           and Accounting Officer)

/S/ ROBERT MAGINN                        Director
---------------------
Robert Maginn

                                         Director
---------------------
Charles S. Houser

/S/ IZHAR ARMONY                         Director
---------------------
Izhar Armony

/S/ JOHN JARVE                           Director
---------------------
John Jarve

/S/ CHARLES N. CORFIELD                  Director
---------------------
Charles N. Corfield

/S/ CHARLES M. SKIBO                     Director
---------------------
Charles M. Skibo

                                         Director
---------------------
Carl Redfield
-7-

                                  EXHIBIT INDEX

EXHIBIT NO.                                 DESCRIPTION OF DOCUMENTS

         4.1      Amended and Restated Certificate of Incorporation of the
                  Registrant, incorporated by reference to Exhibit No. 3.1 to
                  the Registrant's Registration Statement on Form S-1 (file No.
                  333-85545), filed on November 9, 1999.

         4.2.     Amended and Restated By-Laws of the Registrant, incorporated
                  by reference to Exhibit No. 3.2 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-85545).

         4.3      1997 Stock Incentive Plan, incorporated by reference to
                  Exhibit No. 10.8 to the Registrant's Registration Statement on
                  Form S-1 (No. 333-85545).

         4.4      1999 Employee Stock Purchase Plan, as amended, incorporated
                  by reference to Exhibit No. 10.26 to the Registrant's
                  Registration Statement on Form S-1 (No. 333-96533), filed
                  February 10, 2000.

         5        Opinion of Bingham Dana LLP as to the legality of the
                  securities being registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of Bingham Dana LLP (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this
                  Registration Statement).