<PAGE>


   As filed with the Securities and Exchange Commission on November 16, 2001.
                                                    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
                            (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:
                             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                 3,300,000             $0.70            $2,310,000           $577.50
==================================================================================================================
</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 November 13, 2001.


<PAGE>
                                      -2-


                                  INTRODUCTION

         This Registration Statement on Form S-8 is filed by iBasis, Inc., a
Delaware corporation (the "REGISTRANT"), in connection with the registration of
3,300,000 shares (the "SHARES") of common stock, par value $0.001 per share, of
the Registrant (the "COMMON STOCK"), which are in addition to the 5,700,000
shares of Common Stock under the 1997 Stock Incentive Plan that were registered
on the Registrant's Form S-8 filed on February 17, 2000 (File No. 333- 30642)
(the "INITIAL REGISTRATION STATEMENT"). Pursuant to General Instruction E of
Form S-8, the contents of the Initial Registration Statement, to the extent
relating to the registration of the Shares and except as otherwise set forth in
this Registration Statement, are incorporated by reference herein.


<PAGE>
                                      -3-


ITEM 8.  EXHIBITS.

         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), filed on
                  November 9, 1999.

         4.3      1997 Stock Incentive Plan, as amended, incorporated by
                  reference to Exhibit No. 10.8 to the Registrant's Registration
                  Statement on Form S-1 (No. 333-85545), filed on November 9,
                  1999.

         4.4      Third Amendment to 1997 Stock Incentive Plan.

         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).


<PAGE>
                                      -4-


                                   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 November 2001.

                                      iBASIS, INC.


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


<PAGE>
                                      -5-


                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoints Ofer Gneezy
and Richard Tennant, 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 November 2001.

<TABLE>
<CAPTION>

  SIGNATURE                                                                    TITLE
  ---------                                                                   -------
<S>                                                      <C>

                                                          President, Chief Executive Officer and
/s/ OFER GNEEZY                                           Director (Principal Executive Officer)
------------------------------------
    Ofer Gneezy
                                                          Chief Financial  Officer  (Principal  Financial
/s/ RICHARD TENNANT                                       and Accounting Officer)
------------------------------------
    Richard Tennant
                                                          Executive Vice President and Director
/s/ GORDON J. VANDERBRUG
------------------------------------
    Gordon J. VanderBrug
                                                          Director
/s/ CHARLES M. SKIBO
------------------------------------
    Charles M. Skibo
                                                          Director
/s/ W. FRANK KING
------------------------------------
    W. Frank King
</TABLE>


<PAGE>
                                      -6-


                                  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), filed on
                  November 9, 1999.

         4.3      1997 Stock Incentive Plan, as amended, incorporated by
                  reference to Exhibit No. 10.8 to the Registrant's Registration
                  Statement on Form S-1 (No. 333-85545), filed on November 9,
                  1999.

         4.4      Third Amendment to 1997 Stock Incentive Plan.

         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", "filename": "a2063357zs-8.txt", "description": "FORM S-8", "secsgml_size_bytes": 10793}]
{"company-data": {"conformed-name": "IBASIS INC", "cik": "0001091756", "assigned-sic": "7389", "irs-number": "043332534", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-73492", "film-number": "1793898"}, "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 November 16, 2001.
                                                    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
                            (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:
                             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                 3,300,000             $0.70            $2,310,000           $577.50
==================================================================================================================
(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 November 13, 2001.
-2-

                                  INTRODUCTION

         This Registration Statement on Form S-8 is filed by iBasis, Inc., a
Delaware corporation (the "REGISTRANT"), in connection with the registration of
3,300,000 shares (the "SHARES") of common stock, par value $0.001 per share, of
the Registrant (the "COMMON STOCK"), which are in addition to the 5,700,000
shares of Common Stock under the 1997 Stock Incentive Plan that were registered
on the Registrant's Form S-8 filed on February 17, 2000 (File No. 333- 30642)
(the "INITIAL REGISTRATION STATEMENT"). Pursuant to General Instruction E of
Form S-8, the contents of the Initial Registration Statement, to the extent
relating to the registration of the Shares and except as otherwise set forth in
this Registration Statement, are incorporated by reference herein.
-3-

ITEM 8.  EXHIBITS.

         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), filed on
                  November 9, 1999.

         4.3      1997 Stock Incentive Plan, as amended, incorporated by
                  reference to Exhibit No. 10.8 to the Registrant's Registration
                  Statement on Form S-1 (No. 333-85545), filed on November 9,
                  1999.

         4.4      Third Amendment to 1997 Stock Incentive Plan.

         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).
-4-

                                   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 November 2001.

                                      iBASIS, INC.

                                      By: /s/ OFER GNEEZY
                                          -------------------------------------
                                          Ofer Gneezy
                                          President and Chief Executive Officer
-5-

                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoints Ofer Gneezy
and Richard Tennant, 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 November 2001.
SIGNATURE                                                                    TITLE
  ---------                                                                   -------
President, Chief Executive Officer and
/s/ OFER GNEEZY                                           Director (Principal Executive Officer)
------------------------------------
    Ofer Gneezy
                                                          Chief Financial  Officer  (Principal  Financial
/s/ RICHARD TENNANT                                       and Accounting Officer)
------------------------------------
    Richard Tennant
                                                          Executive Vice President and Director
/s/ GORDON J. VANDERBRUG
------------------------------------
    Gordon J. VanderBrug
                                                          Director
/s/ CHARLES M. SKIBO
------------------------------------
    Charles M. Skibo
                                                          Director
/s/ W. FRANK KING
------------------------------------
    W. Frank King
-6-

                                  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), filed on
                  November 9, 1999.

         4.3      1997 Stock Incentive Plan, as amended, incorporated by
                  reference to Exhibit No. 10.8 to the Registrant's Registration
                  Statement on Form S-1 (No. 333-85545), filed on November 9,
                  1999.

         4.4      Third Amendment to 1997 Stock Incentive Plan.

         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).