March 30, 2000

AT&T Corp.
295 North Maple Avenue
Basking Ridge, NJ  07920

IDT Corporation
520 Broad Street
Newark, New Jersey  07102

               Re:  Purchase of Class A common stock
                    and related transactions

Gentlemen:

This letter agreement (this "Agreement") will confirm the actions taken by the
Board of Directors (the "Board") of Net2Phone, Inc. (the "Company"), and by a
committee of independent directors of the Company to whom authority was duly
delegated by the Board, in connection with and in consideration for the proposed
purchase (the "Purchase") by AT&T Corp. ("AT&T") and its designees, through a
newly formed business entity ("Holdco"), from IDT Corporation ("IDT") of
14,900,000 shares of Class A common stock, par value $.01 per share (the "Class
A Stock"), of the Company and certain related transactions, as set forth in the
Letter Agreement, dated March 28, 2000, between AT&T and IDT (the "Letter
Agreement").

1.   Board Approval of the Amendment. The Board has duly adopted a resolution
     setting forth amendments (the





     "Amendments") to the Company's certificate of incorporation (i) increasing
     the number of authorized shares of Class A Stock by four million and (ii)
     notwithstanding Section 4 of the Letter Agreement, expanding the Board by
     two seats, and resolving to nominate designees named by AT&T to such
     additional two seats. Promptly after the closing of the Purchase, IDT shall
     cause one of its designated Board members to resign, and AT&T shall
     nominate the replacement designee. AT&T and IDT agree to use their
     reasonable best efforts to assure that at least five members of the Board
     will be members not employed by, providing material services for
     compensation to or otherwise affiliated with AT&T, IDT or any member of
     Holdco or any of their affiliates (the "disinterested directors"); provided
     that the requirement for such reasonable efforts by AT&T and IDT shall
     cease to apply at such time as Holdco or IDT, as the case may be, becomes
     the beneficial owner of more than 85% or less than 15% of the voting power
     of the Company.

2.   Solicitation of Shareholder Approval. The Board has declared the
     advisability of the Amendments and called a special meeting of the
     Company's stockholders for the consideration of the Amendments. The Board,
     subject to its fiduciary obligations, shall promptly take such actions as
     are necessary and appropriate to cause the adoption of the Amendments,
     including causing an information or proxy statement containing the
     recommendation of the Board of Directors in favor of the Amendments to be
     distributed to stockholders as promptly as practicable. The only additional
     corporate action required for the Primary Issuance is the approval of the
     Amendments by the affirmative vote of the holders of at least 66-2/3% of
     the outstanding Common Shares (as defined in Article Fourth of the
     Company's certificate of incorporation) and the filing of the Amendments
     with the Secretary of State of Delaware.

3.   Section 203 of the Delaware General Corporation Law. By resolution, the
     Board has confirmed that the restrictions contained in Section 203 of the
     Delaware General Corporation Law shall not apply to any business
     combination between the Company and AT&T or Holdco.

4.   Primary Issuance. Upon adoption of the Amendments, subject to the
     satisfaction or waiver of the terms and conditions set forth in clauses (2)
     through (10) of Section 3 of the





     Letter Agreement, and subject to the parties to the Letter Agreement being
     ready, willing and able to consummate the Purchase, the Company shall
     promptly issue and sell to Holdco, and Holdco will purchase, four million
     shares of Class A Stock (the "Primary Issuance") for a price of $75 per
     share. A result of the Primary Issuance will be to cause Holdco to become a
     Holder within the meaning of Article Fourth, Section 3(e)(2) of the
     Company's certificate of incorporation, with the effect that the shares of
     Class A Stock to be sold to Holdco by IDT under the Letter Agreement will
     not be converted by their terms into shares of Common Stock, par value $.01
     per share, of the Company upon the consummation of the Purchase.

5.   "Piggyback" Registration Rights. The Board has granted to Holdco demand and
     "piggyback" registration rights with respect to the shares of capital stock
     of the Company hereafter acquired by it from IDT under the Letter
     Agreement, substantially as provided in the form of the Registration Rights
     Agreement attached hereto as Exhibit A.

6.   Stock Option and Incentive Plan. The Board has adopted a resolution
     amending Section 6(g) of the Company's Amended and Restated 1999 Stock
     Option and Incentive Plan (the "Plan"), and any other sections of the Plan
     necessary to ensure that no rights of IDT employees under the Plan will be
     terminated or affected in any way as a result of the transactions
     contemplated in the Letter Agreement.

7.   License and Approval of Transactions by Disinterested Directors. (a) The
     Company will grant (i) to AT&T, a license for all of the Company's present
     and future technology for use in the present and future businesses of AT&T
     and its affiliates and (ii) to IDT, a license for all of the Company's
     present and future technology for use in the present and future businesses
     of IDT and its affiliates. The Company also agrees that should the terms,
     conditions and pricing of a license be given prior to, on or after the date
     of the Letter Agreement by the Company to any other person (including, in
     the case of AT&T, IDT, and in the case of IDT, AT&T) which are more
     favorable to the licensee than those given to AT&T or IDT, as the case may
     be, which license has been approved or ratified by a majority of the
     disinterested directors, such terms, conditions and pricing shall be
     applicable to AT&T's





     license or IDT's license, as the case may be, at such party's option. The
     Company agrees that licenses granted by it shall in all cases be subject to
     approval or ratification by a majority of the disinterested directors.

     (b) Any contract or transaction, including a license, between AT&T or any
     other participant in Holdco or any of their affiliates and the Company, or
     between IDT or any of its affiliates and the Company, involving the
     potential payment to or from the Company of more than $500,000, or any
     business combination between the Company, on the one hand, and IDT, AT&T,
     any participant in Holdco or any of their affiliates, on the other hand,
     shall be subject to the approval of a majority of the disinterested
     directors of the Company; provided that the requirement for such approval
     shall cease to apply at such time as Holdco or IDT, as the case may be,
     becomes the beneficial owner of more than 85% or less than 15% of the
     voting power of the Company; and provided further that the requirement of
     disinterested director approval shall not be required with respect to the
     granting of a license by the Company to AT&T or IDT which does not contain
     terms, conditions and pricing that are more favorable to the licensee than
     those contained in a license granted to any other person, which license has
     been approved or ratified by a majority of disinterested directors.

     (c) This Section 7 supersedes Section 11 of the Letter Agreement, other
     than the first sentence of Section 11 of the Letter Agreement which remains
     in full force and effect.

8.   AT&T/Company Arrangements. AT&T and the Company will support good faith
     negotiations to work together to enter into the following commercial
     arrangements:

     o   AT&T will offer the Company's service on the WorldNet Internet service.

     o   Each of AT&T and the Company will be classified by the other party as a
         "Preferred Supplier" where mutually beneficial and not inconsistent
         with other commitments of the parties existing on the date of this
         Agreement, with respect to all services offered by the parties. AT&T
         will make available to the Company the





         opportunity to make presentations to senior operational management of
         AT&T with respect to products offered by the Company.

     o   AT&T and the Company will work together to develop and deploy new
         products and applications that integrate Voice over Internet Protocol
         (VoIP) technology into PBX's and other communication products for the
         business market.

     o   AT&T and the Company will work together to develop a series of
         commercial and VoIP technology developmental agreements. The goal of
         the agreements will be to (i) establish a framework for working
         together to further develop and enhance each of AT&T's and the
         Company's VoIP technology, and (ii) jointly develop new VoIP products
         and services.

     o   AT&T and the Company will work together to develop broadband
         applications using VoIP technology, it being understood that it is not
         the intent of the parties to create a preferred position for the
         Company as a broadband services provider.

     o   AT&T and the Company will work together in developing and implementing
         such technologies as are required for the interoperability of each
         party's services with the other's.

     o   AT&T and the Company will work together in developing "on-net"
         advantages in the delivery of each other's services.

     o   AT&T and the Company will work together to develop and evolve the
         standards for Internet telephony.

9.   Voting Agreement. In the event that Holdco and IDT are unable to agree on
     acceptable nominees to the Board (as described in Section 9 of the Letter
     Agreement), Holdco and IDT will be counted as present for purposes of
     determining a quorum at the shareholders meeting but will abstain from
     voting on such nominees as to which Holdco and IDT are unable to agree.





10.  Binding Intent. It is the intent of the parties hereto that the agreements
     contained herein be legally binding on and enforceable against them. This
     Agreement will be governed by and construed in accordance with the laws of
     the State of New York applicable to contracts executed in and to be fully
     performed in such State, without giving effect to its conflicts of law
     rules or principles. Each party hereto (a) consents to submit itself to the
     personal jurisdiction of any federal court located in the State of New York
     or any New York state court in the event any dispute arises out of this
     Agreement or any of the transactions contemplated by this Agreement, (b)
     agrees that it will not attempt to deny such personal jurisdiction by
     motion or other request for leave from any such court and (c) agrees that
     it will not bring any action relating to this Agreement or any of the
     transactions contemplated by this Agreement in any court other than a
     federal or state court sitting in the State of New York. The invalidity or
     unenforceability of any provision of this Agreement shall not affect the
     validity or enforceability of any other provision of this Agreement, which
     shall remain in full force and effect.

11.  Definitive Documentation. The parties agree to negotiate in good faith and
     enter into mutually acceptable definitive documentation with respect to the
     transactions contemplated herein and in the Letter Agreement and on the
     terms and conditions set forth herein and in the Letter Agreement.





If the foregoing conforms to your understanding, please so signify by signing in
the space provided below. This Agreement may be executed in one or more
counterparts, each of which shall be deemed to be an original, but all of which
shall constitute one and the same agreement.

                                          Very truly yours,


                                          NET2PHONE, INC.

                                          By: /s/ HOWARD S. BALTER
                                             -----------------------

Accepted and Agreed:
AT&T CORP.

By: /s/ JOHN C. PETRILLO
   ---------------------

IDT CORPORATION

By:/s/ JAMES A. COURTER
   ---------------------