<PAGE>

                                                           Registration No. 333-

    As filed with the Securities and Exchange Commission on August 26, 1999


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

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                                   FORM S-8

                            REGISTRATION STATEMENT
                                    UNDER
                          THE SECURITIES ACT OF 1933

                                Net2Phone, Inc.
            ------------------------------------------------------
            (Exact Name of Registrant as Specified in Its Charter)

        Delaware                                     22-3559037
 ------------------------           ------------------------------------------
 (State of Incorporation)               (I.R.S. Employer Identification No.)

                                171 Main Street
                         Hackensack, New Jersey 07601
        --------------------------------------------------------------
         (Address of Principal Executive Offices, Including Zip Code)

 Amended and Restated 1999 Stock Option and Incentive Plan of Net2Phone, Inc.
  ---------------------------------------------------------------------------
                           (Full Title of the Plan)

                               Howard S. Balter
                            Chief Executive Officer
                                Net2Phone, Inc.
                                171 Main Street
                         Hackensack, New Jersey 07601
                                (201) 907-5304
           -------------------------------------------------------
          (Name, Address and Telephone Number, Including Area Code,
                             of Agent for Service)

                                  Copies to:
                             Ira Greenstein, Esq.
                            Morrison & Foerster LLP
                          1290 Avenue of the Americas
                           New York, New York 10104
                                (212) 468-8000

                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
=========================================================================================================================
                                                          Proposed Maximum      Proposed Maximum       Amount of
Title of Securities               Amount to  be           Offering Price        Aggregate Offering     Registration
to be Registered(1)               Registered(1)           Per Share (2)         Price (2)              Fee
-------------------------------------------------------------------------------------------------------------------------
<S>                               <C>                     <C>                   <C>                    <C>
Common Stock,
par value                         9,569,782               $26.94                $257,809,927           $71,671
$.01 per
share
=========================================================================================================================
</TABLE>
(1)  Includes 9,569,782 shares to be registered under the Registrant's Amended
     and Restated 1999 Stock Option and Incentive Plan, plus such additional
     indeterminate number of shares of the Common Stock as may be issuable
     pursuant to certain antidilution adjustment provisions thereof.
(2)  Estimated pursuant to Rules 457(c) and (h) under the Securities Act of
     1933, as amended, based on the average of the high and low prices of the
     Common Stock on the Nasdaq National Market on August 19, 1999.

================================================================================
<PAGE>

                                    PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Certain Documents By Reference.

     The following documents filed with the Securities and Exchange Commission
(the "Commission") by the registrant, Net2Phone, Inc., a Delaware corporation
(the "Company"), pursuant to the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), are incorporated by reference in this registration
statement.

     (a) The description of the common stock, par value $.01 per share (the
     "Common Stock"), of the Company set forth as Item 1 under the caption
     "Description of Securities" in the Company's Registration Statement on Form
     8-A, dated July 20, 1999, filed pursuant to Section 12(g) of the Exchange
     Act and declared effective by the Commission on July 29, 1999, including
     any amendment or report filed for the purpose of updating such information.

     (b) The Registrant's Prospectus filed with the Commission pursuant to Rule
     424(b) on July 30, 1999.

     All documents subsequently filed by the Company pursuant to Sections 13(a),
13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a post-effective
amendment, which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed to be
incorporated by reference herein and to be a part hereof from the date of filing
of such documents.  Any statement contained in a document incorporated or deemed
to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes of this registration statement to the extent that a
statement contained herein or in any other subsequently filed document which
also is incorporated or deemed to be incorporated by reference herein modifies
or supersedes such statement.  Any such statement so modified or superseded
shall not be deemed, except as so modified or superseded, to constitute a part
of this registration statement.

Item 4.   Description of Securities.

     Not applicable.

Item 5.   Interests of Named Experts and Counsel.

     Certain legal matters with respect to the Common Stock will be passed on by
Morrison & Foerster LLP.

Item 6.   Indemnification of Directors and Officers.

     Reference is made to Section 145 of the Delaware General Corporation Law,
which provides for indemnification of directors, officers and other employees in
certain circumstances, and to Section 102(b)(7) of the Delaware General
Corporation Law, which provides for the elimination or limitation of the
personal liability for monetary damages of directors under certain
circumstances. Article Sixth of the Company's certificate of incorporation, as
amended and restated, eliminates the personal liability for monetary damages of
directors under certain circumstances.  The Company's bylaws provide
indemnification to our directors and officers to the fullest extent permitted by
the Delaware General

                                     II-1
<PAGE>

Corporation Law for, among other things, liabilities for judgments in and
settlements of lawsuits and other proceedings and for the advance and payment of
fees and expenses reasonably incurred by the director or officer in defense of
any such lawsuit or proceeding.

Item 7.         Exemption from Registration Claimed.

     Not applicable.

Item 8.         Exhibits.

     4.1        Restated Certificate of Incorporation of the Company
                (incorporated by reference to Exhibits 3.3 and 3.4 to the
                Registration Statement on Form S-1 of the Company (File No. 333-
                78713)).

     4.2        By-Laws of the Company (incorporated by reference to Exhibit 3.2
                to the Registration Statement on Form S-1 of the Company (File
                No. 333-78713)).

     *5.1       Legal Opinion of Morrison & Foerster LLP.

     *23.1      Consent of Morrison & Foerster LLP. (included in Exhibit 5.1
                hereto).

     *23.2      Consent of Ernst & Young LLP.

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

     * Filed herewith.

Item 9.         Undertakings.

      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 that is incorporated by reference in this 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.

      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 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 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.



                                     II-2
<PAGE>

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, 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 City of Hackensack, State of New Jersey, on this 26th day of
August, 1999.

                              NET2PHONE, INC.

                              By  /s/ Howard S. Balter
                                  --------------------
                                  Howard S. Balter
                                  Chief Executive Officer


     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.

<TABLE>
<CAPTION>
         Signature                               Titles                              Date
         ---------                               ------                              ----
<S>                           <C>                                            <C>

/s/ Clifford M. Sobel                     Chairman of the Board              August 26, 1999
----------------------------
Clifford M. Sobel

/s/ Howard S. Balter              Chief Executive Officer and Director       August 26, 1999
----------------------------          (Principal Executive Officer)
Howard S. Balter

/s/ Ilan M. Slasky                 Chief Financial Officer (Principal        August 26, 1999
----------------------------        Accounting and Financial Officer)
Ilan M. Slasky

/s/ James R. Mellor                             Director                     August 26, 1999
----------------------------
James R. Mellor

/s/ Howard S. Jonas                             Director                     August 26, 1999
----------------------------
Howard S. Jonas

/s/ Gary E. Rieschel                            Director                     August 26, 1999
----------------------------
Gary E. Rieschel

/s/ James A. Courter                            Director                     August 26, 1999
----------------------------
James A. Courter

/s/ Stephen A. Oxman                            Director                     August 26, 1999
----------------------------
Stephen A. Oxman

/s/ Jesse P. King                               Director                     August 26, 1999
----------------------------
Jesse P. King
</TABLE>

                                     II-3
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 12233}]
{"company-data": {"conformed-name": "NET2PHONE INC", "cik": "0001086472", "assigned-sic": "4813", "irs-number": "223559037", "state-of-incorporation": "DE", "fiscal-year-end": "0731"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-85945", "film-number": "99700058"}, "business-address": {"street1": "17 MAIN STREET", "city": "HACKENSACK", "state": "NJ", "zip": "07601", "phone": "2019282990"}, "mail-address": {"street1": "17 MAIN STREET", "city": "HACKENSACK", "state": "NJ", "zip": "07601"}}
Registration No. 333-

    As filed with the Securities and Exchange Commission on August 26, 1999

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

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                                   FORM S-8

                            REGISTRATION STATEMENT
                                    UNDER
                          THE SECURITIES ACT OF 1933

                                Net2Phone, Inc.
            ------------------------------------------------------
            (Exact Name of Registrant as Specified in Its Charter)

        Delaware                                     22-3559037
 ------------------------           ------------------------------------------
 (State of Incorporation)               (I.R.S. Employer Identification No.)

                                171 Main Street
                         Hackensack, New Jersey 07601
        --------------------------------------------------------------
         (Address of Principal Executive Offices, Including Zip Code)

 Amended and Restated 1999 Stock Option and Incentive Plan of Net2Phone, Inc.
  ---------------------------------------------------------------------------
                           (Full Title of the Plan)

                               Howard S. Balter
                            Chief Executive Officer
                                Net2Phone, Inc.
                                171 Main Street
                         Hackensack, New Jersey 07601
                                (201) 907-5304
           -------------------------------------------------------
          (Name, Address and Telephone Number, Including Area Code,
                             of Agent for Service)

                                  Copies to:
                             Ira Greenstein, Esq.
                            Morrison & Foerster LLP
                          1290 Avenue of the Americas
                           New York, New York 10104
                                (212) 468-8000

                        CALCULATION OF REGISTRATION FEE
=========================================================================================================================
                                                          Proposed Maximum      Proposed Maximum       Amount of
Title of Securities               Amount to  be           Offering Price        Aggregate Offering     Registration
to be Registered(1)               Registered(1)           Per Share (2)         Price (2)              Fee
-------------------------------------------------------------------------------------------------------------------------
Common Stock,
par value                         9,569,782               $26.94                $257,809,927           $71,671
$.01 per
share
=========================================================================================================================
(1)  Includes 9,569,782 shares to be registered under the Registrant's Amended
     and Restated 1999 Stock Option and Incentive Plan, plus such additional
     indeterminate number of shares of the Common Stock as may be issuable
     pursuant to certain antidilution adjustment provisions thereof.
(2)  Estimated pursuant to Rules 457(c) and (h) under the Securities Act of
     1933, as amended, based on the average of the high and low prices of the
     Common Stock on the Nasdaq National Market on August 19, 1999.

================================================================================
PART II

              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Certain Documents By Reference.

     The following documents filed with the Securities and Exchange Commission
(the "Commission") by the registrant, Net2Phone, Inc., a Delaware corporation
(the "Company"), pursuant to the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), are incorporated by reference in this registration
statement.

     (a) The description of the common stock, par value $.01 per share (the
     "Common Stock"), of the Company set forth as Item 1 under the caption
     "Description of Securities" in the Company's Registration Statement on Form
     8-A, dated July 20, 1999, filed pursuant to Section 12(g) of the Exchange
     Act and declared effective by the Commission on July 29, 1999, including
     any amendment or report filed for the purpose of updating such information.

     (b) The Registrant's Prospectus filed with the Commission pursuant to Rule
     424(b) on July 30, 1999.

     All documents subsequently filed by the Company pursuant to Sections 13(a),
13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a post-effective
amendment, which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed to be
incorporated by reference herein and to be a part hereof from the date of filing
of such documents.  Any statement contained in a document incorporated or deemed
to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes of this registration statement to the extent that a
statement contained herein or in any other subsequently filed document which
also is incorporated or deemed to be incorporated by reference herein modifies
or supersedes such statement.  Any such statement so modified or superseded
shall not be deemed, except as so modified or superseded, to constitute a part
of this registration statement.

Item 4.   Description of Securities.

     Not applicable.

Item 5.   Interests of Named Experts and Counsel.

     Certain legal matters with respect to the Common Stock will be passed on by
Morrison & Foerster LLP.

Item 6.   Indemnification of Directors and Officers.

     Reference is made to Section 145 of the Delaware General Corporation Law,
which provides for indemnification of directors, officers and other employees in
certain circumstances, and to Section 102(b)(7) of the Delaware General
Corporation Law, which provides for the elimination or limitation of the
personal liability for monetary damages of directors under certain
circumstances. Article Sixth of the Company's certificate of incorporation, as
amended and restated, eliminates the personal liability for monetary damages of
directors under certain circumstances.  The Company's bylaws provide
indemnification to our directors and officers to the fullest extent permitted by
the Delaware General

                                     II-1
Corporation Law for, among other things, liabilities for judgments in and
settlements of lawsuits and other proceedings and for the advance and payment of
fees and expenses reasonably incurred by the director or officer in defense of
any such lawsuit or proceeding.

Item 7.         Exemption from Registration Claimed.

     Not applicable.

Item 8.         Exhibits.

     4.1        Restated Certificate of Incorporation of the Company
                (incorporated by reference to Exhibits 3.3 and 3.4 to the
                Registration Statement on Form S-1 of the Company (File No. 333-
                78713)).

     4.2        By-Laws of the Company (incorporated by reference to Exhibit 3.2
                to the Registration Statement on Form S-1 of the Company (File
                No. 333-78713)).

     *5.1       Legal Opinion of Morrison & Foerster LLP.

     *23.1      Consent of Morrison & Foerster LLP. (included in Exhibit 5.1
                hereto).

     *23.2      Consent of Ernst & Young LLP.

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

     * Filed herewith.

Item 9.         Undertakings.

      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 that is incorporated by reference in this 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.

      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 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 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.

                                     II-2
SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, 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 City of Hackensack, State of New Jersey, on this 26th day of
August, 1999.

                              NET2PHONE, INC.

                              By  /s/ Howard S. Balter
                                  --------------------
                                  Howard S. Balter
                                  Chief Executive Officer

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.
Signature                               Titles                              Date
         ---------                               ------                              ----
/s/ Clifford M. Sobel                     Chairman of the Board              August 26, 1999
----------------------------
Clifford M. Sobel

/s/ Howard S. Balter              Chief Executive Officer and Director       August 26, 1999
----------------------------          (Principal Executive Officer)
Howard S. Balter

/s/ Ilan M. Slasky                 Chief Financial Officer (Principal        August 26, 1999
----------------------------        Accounting and Financial Officer)
Ilan M. Slasky

/s/ James R. Mellor                             Director                     August 26, 1999
----------------------------
James R. Mellor

/s/ Howard S. Jonas                             Director                     August 26, 1999
----------------------------
Howard S. Jonas

/s/ Gary E. Rieschel                            Director                     August 26, 1999
----------------------------
Gary E. Rieschel

/s/ James A. Courter                            Director                     August 26, 1999
----------------------------
James A. Courter

/s/ Stephen A. Oxman                            Director                     August 26, 1999
----------------------------
Stephen A. Oxman

/s/ Jesse P. King                               Director                     August 26, 1999
----------------------------
Jesse P. King
II-3