Document:

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                                                                   Exhibit 10.48

                          REGISTRATION RIGHTS AGREEMENT

         This Registration Rights Agreement (the "Agreement") is entered into as
of March 30, 2000 by and between Net2Phone, Inc., a Delaware corporation (the
"Company"), and Yahoo! Inc, a Delaware corporation (the "Stockholder").

                                    RECITALS

         The Company and the Stockholder have entered into a Stock Exchange
Agreement of even date herewith (the "Exchange Agreement"), which provides for
the exchange of 2,777,778 shares of the Company's Common Stock (the "Shares")
for 806,452 shares of the Stockholder's Common Stock. In connection with the
Stockholder's execution of the Exchange Agreement, the Stockholder desires to
obtain and the Company has agreed to grant certain registration rights to the
Stockholder with respect to the Shares.

                                    AGREEMENT

         The parties hereby agree as follows:

         1.       REGISTRATION RIGHTS.

                  1.1      DEFINITIONS.  For purposes of this Section 1:

                           (a) The terms "register," "registered," and
"registration" refer to a registration effected by preparing and filing a
registration statement or similar document in compliance with the Securities Act
of 1933, as amended (the "Securities Act"), and the subsequent declaration or
ordering of the effectiveness of such registration statement or document.

                           (b) The term "Registrable Securities" means:

                                    (i)     the Shares; and

                                    (ii) any other shares of Common Stock of the
Company issued as (or issuable upon the conversion or exercise of any warrant,
right or other security which is issued as) a dividend or other distribution
with respect to, or in connection with a stock split, or in exchange for or in
replacement of, the Shares, excluding in all cases, however, any Registrable
Securities sold by a person in a transaction in which his or her rights under
this Agreement are not assigned; provided, however, that Common Stock or other
securities shall only be treated as Registrable Securities if and so long as
they have not been sold to or through a broker or dealer or underwriter in a
public distribution or a public securities transaction.

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                           (c) The term "Holder" means the Stockholder, its
successors and assigns.

                           (d) The term "SEC" means the Securities and Exchange
Commission.

                  1.2      REQUEST FOR REGISTRATION.

                           (a) If one or more of the following events shall
occur: (i) the failure of the Company and the Stockholder to enter into on or
before April 30, 2000 a definitive commercial agreement (the "Commercial
Agreement") pursuant to that certain letter of intent of even date herewith
between the parties hereto, in form and substance reasonably satisfactory to
such parties, after negotiating in good faith with the intention of completing
such agreement, (ii) the termination by Yahoo! of the Commercial Agreement
following a breach of such agreement by the Company, in accordance with the
terms and conditions thereof, or (iii) the effective date of a "Change in
Control" of the Company (as defined below), and following such occurrence, the
Holder shall send to the Company a written request that the Company file a
registration statement under the Securities Act covering the registration of any
or all of the Registrable Securities, then the Company shall use its best
efforts to effect as expeditiously as may be practicable the registration under
the Securities Act of all Registrable Securities which the Holder requests to be
registered. Notwithstanding the foregoing, the Company shall not be required to
effect any registration if the Registrable Securities that the Company shall
have been requested to register shall, in the aggregate, have a current market
value of less than (x) $5,000,000 if the Registrable Securities are to be
registered on Form S-1 (or any successor form thereto) or (y) $1,000,000 if the
Registrable Securities are to be registered on Form S-3 (or any successor form
thereto). The Holder shall have the right to only one (1) registration pursuant
to this Section 1.2(a). For purposes of this Agreement, a "Change in Control" of
the Company shall mean the sale, conveyance or other disposition by the Company
of all or substantially all of its property or business or the Company's merger
with or into or consolidation with any other corporation (other than a
wholly-owned subsidiary corporation) or the consummation of any other
transaction or series of related transactions in which more than 50% of the
voting power of the Company is disposed of, or the execution by the Company of
any binding agreement providing for any of the foregoing transactions: provided,
however, that the sale, disposition or conveyance of all or a portion of the
Company's stock or assets to, or the merger or consolidation of the Company
with, AT&T Corp. or any of its wholly owned subsidiaries, or the execution of a
binding agreement providing for the foregoing with AT&T Corp. or any of its
wholly owned subsidiaries, shall not constitute a Change in Control for purposes
of this Section 1.2.

                           (b) If the Holder intends to distribute the
Registrable Securities covered by their request by means of an underwriting, it
shall so advise the Company as a part of its request made pursuant to this
Section 1.2. The underwriter will be selected by the Holder, subject to the
Company's approval, which shall not be unreasonably

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withheld. Thereafter, the Holder and the Company shall enter into an
underwriting agreement in customary form with the underwriter or underwriters
selected for such underwriting.

                           (c) Notwithstanding the foregoing, if the Company
shall furnish to the Holder a certificate signed by the President of the Company
stating that in the good faith judgment of the Board of Directors of the
Company, it would be materially detrimental to the Company and its stockholders
for such registration statement to be filed and it is therefore essential to
defer the filing of such registration statement, the Company shall have the
right to defer such filing for a reasonable period of time (but not more than 90
days) after receipt of the request of the Holder (the "Demand Blackout Period").
The Company shall give the Holder prompt written notice of any such
determination to defer filing in the form of a certificate signed by an
executive officer of the Company. The Company shall promptly notify the Holder
of the expiration or earlier termination of the Demand Blackout Period.

                  1.3 COMPANY REGISTRATION. If (but without any obligation to do
so) the Company proposes to register (including for this purpose a registration
effected by the Company for any Company stockholder other than the Holder) any
of its stock under the Securities Act in connection with the public offering of
such securities solely for cash (other than a registration relating solely to
the sale of securities to participants in a Company stock plan or a transaction
covered by Rule 145 under the Securities Act, a registration in which the only
stock being registered is Common Stock issuable upon conversion of debt
securities which are also being registered, or any registration on any form
which does not include substantially the same information as would be required
to be included in a registration statement covering the sale of the Registrable
Securities), the Company shall, at such time, promptly give the Holder written
notice of such registration. Upon the written request of the Holder given within
twenty (20) days after mailing of such notice by the Company, the Company shall,
subject to the provisions of Section 1.5, cause to be registered under the
Securities Act all of the Registrable Securities that the Holder has requested
to be registered. Nothing in this Section 1.3 shall create any liability on the
part of the Company or any other person to the Holder if the Company, for any
reason, decides not to file a registration statement proposed to be filed
pursuant to this Section 1.3 or to withdraw such registration statement
subsequent to its filing (except for the Company's obligation to pay the
expenses in connection therewith as provided in Section 1.11), regardless of any
action whatsoever that the Holder may have taken, whether as a result of the
issuance by the Company of any notice under this Section 1.3. or otherwise.

                  1.4 OBLIGATIONS OF THE COMPANY. Whenever required under this
Section 1 to effect the registration of any Registrable Securities, the Company
shall, as expeditiously as reasonably possible:

                           (a) Prepare and file with the SEC a registration
statement with respect to such Registrable Securities and use its best efforts
to cause such registration

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statement to become effective, and, upon the request the Holder, keep such
registration statement effective for up to 90 days (20 days in the case of a
registration statement filed on Form S-1 under the Securities Act) or such
shorter period during which the Holders complete the distribution described in
the registration statement relating thereto, whichever first occurs.

                           (b) Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Act with respect to the disposition of all securities covered
by such registration statement for up to 90 days;

                           (c) Cause all such Registrable Securities registered
pursuant hereunder to be listed on each securities exchange on which similar
securities issued by the Company are then listed;

                           (d) Furnish to the Holder participating in the
registration such reasonable number of copies of the registration statement,
preliminary prospectus, final prospectus and such other documents as the Holder
may reasonably request;

                           (e) Use its best efforts to register and qualify the
securities covered by such registration statement under such securities or Blue
Sky laws of such jurisdictions as shall be reasonably requested by the Holder,
provided that the Company shall not be required in connection therewith or as a
condition thereto to qualify to do business or to file a general consent to
service of process in any such states or jurisdictions;

                           (f) Notify the Holder at any time when a prospectus
relating thereto is required to be delivered under the Securities Act of the
happening of any event as a result of which the prospectus included in such
registration statement, as then in effect, includes an untrue statement of a
material fact or omits to state a material fact required to be stated therein or
necessary to make the statements therein not misleading in the light of the
circumstances then existing, and at the request of the Holder, prepare and
furnish to the Holder a reasonable number of copies of a supplement to or an
amendment of such prospectuses as may be necessary so that, as thereafter
delivered to the purchasers of such shares, such prospectuses shall not include
an untrue statement of a material fact or omit to state a material fact required
to be stated therein or necessary to make the statements therein no misleading
in light of the circumstances then existing;

                           (g) Provide a transfer agent and registrar for all
Registrable Securities registered pursuant hereunder not later than the
effective date of such registration.

                           (h) Use best efforts to cause the transfer agent to
remove restrictive legends on certificates representing the Registrable
Securities covered by a

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registration statement hereunder, as the Company determines to be appropriate,
upon advice of counsel;

                           (i) In the event of any underwritten public offering
hereunder, enter into and perform its obligations under an underwriting
agreement, in usual and customary form, with the managing underwriter of such
offering. The Holder shall also enter into and perform its obligations under
such an agreement; and

                           (j) Use its best efforts to furnish, at the request
of the Holder, on the date that the Registrable Securities are delivered to the
underwriters for sale in connection with a registration pursuant to this Section
1, if such securities are being sold through underwriters, or, if such
securities are not being sold through underwriters, on the date that the
registration statement with respect to such securities becomes effective, (i) an
opinion, dated such date, of the counsel representing the Company for the
purposes of such registration, in form and substance as is customarily given to
underwriters in an underwritten public offering, addressed to the underwriters,
if any, and to the Holder and (ii) a letter dated such date, from the
independent certified public accountants of the Company, in form and substance
as is customarily given by independent certified public accountants to
underwriters in an underwritten public offering, addressed to the underwriters,
if any, and to the Holder.

                  1.5 UNDERWRITING REQUIREMENTS. In connection with any offering
involving an underwriting of shares of the Company's capital stock, the Company
shall not be required under Section 1.3 to include any of the Holder's
securities in such underwriting unless they accept the terms of the underwriting
as agreed upon between the Company and the underwriters selected by it (or by
other persons entitled to select the underwriters), and then only in such
quantity as the underwriters determine in their sole discretion will not
jeopardize the success of the offering by the Company. If the total amount of
securities, including Registrable Securities, requested by stockholders to be
included in such offering exceeds the amount of securities sold other than by
the Company that the underwriters determine in their sole discretion is
compatible with the success of the offering, then the Company shall be required
to include in the offering only that number of such securities, including
Registrable Securities, which the underwriters determine in their sole
discretion will not jeopardize the success of the offering (the securities so
included to be apportioned pro rata among the selling stockholders according to
the total amount of securities entitled to be included therein owned by each
selling stockholder or in such other proportions as shall mutually be agreed to
by such selling stockholders). The Holder shall not be entitled to participate
in an underwritten offering unless the Holder enters into, and performs its
obligations under, one or more underwriting agreements and any related
agreements and documents (including an escrow agreement and/or a power of
attorney with respect to the disposition of the Registrable Securities), in the
form that the Holder shall agree to with the lead managing underwriter of the
transaction. If the Holder disapproves of the terms of any underwriting, it may
elect, prior to the execution of any underwriting agreement, to withdraw
therefrom by written notice to the Company and the lead managing underwriter.

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                  1.6 DELAY OF REGISTRATION. The Holder shall not have any right
to obtain or seek an injunction restraining or otherwise delaying any
registration as the result of any controversy that might arise with respect to
the interpretation or implementation of this Section 1.

                  1.7 FURNISH INFORMATION. It shall be a condition precedent to
the obligations of the Company to take any action pursuant to this Section 1
with respect to the Registrable Securities of the Holder that the Holder shall
furnish to the Company such information regarding itself, the Registrable
Securities held by it, and the intended method of disposition of such securities
as shall be required to effect the registration of the Holder's Registrable
Securities.

                  1.8 INDEMNIFICATION. In the event any Registrable Securities
are included in a registration statement under this Section 1:

                           (a) To the extent permitted by law, the Company will
indemnify and hold harmless the Holder and each person, if any, who controls the
Holder within the meaning of the Securities Act or the Securities Exchange Act
of 1934, as amended (the "Exchange Act"), against any losses, claims, damages,
or liabilities (joint or several) to which they may become subject, under the
Securities Act, the Exchange Act or other federal or state law, insofar as such
losses, claims, damages, or liabilities (or actions in respect thereof) arise
out of or are based upon any of the following statements, omissions or
violations (collectively a "Violation"): (i) any untrue statement or alleged
untrue statement of a material fact contained in such registration statement,
including any final prospectus contained therein or any amendments or
supplements thereto, (ii) the omission or alleged omission to state therein a
material fact required to be stated therein, or necessary to make the statements
therein not misleading, or (iii) any violation or alleged violation by the
Company of the Securities Act, the Exchange Act, any state securities law or any
rule or regulation promulgated under the Securities Act, the Exchange Act or any
state securities law; and the Company will pay, as incurred, any legal or other
expenses reasonably incurred by them in connection with investigating or
defending any such loss, claim, damage, liability, or action; provided, however,
that the indemnity agreement contained in this subsection 1.8(a) shall not apply
to amounts paid in settlement of any such loss, claim, damage, liability, or
action if such settlement is effected without the consent of the Company, which
consent shall not be unreasonably withheld, nor shall the Company be liable in
any such case for any such loss, claim, damage, liability, or action to the
extent that it arises out of or is based upon a Violation which occurs in
reliance upon and in conformity with written information furnished expressly for
use in connection with such registration by such Holder or controlling person.

                           (b) To the extent permitted by law, the Holder will
indemnify and hold harmless the Company, each of its directors, each of its
officers who has signed the registration statement, each person, if any, who
controls the Company within the meaning of the Securities Act or the Exchange
Act against any losses, claims, damages,

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or liabilities (joint or several) to which any of the foregoing persons may
become subject, under the Securities Act, the Exchange Act or other federal or
state law, insofar as such losses, claims, damages, or liabilities (or actions
in respect thereof) arise out of or are based upon any Violation, in each case
to the extent (and only to the extent) that such Violation occurs in reliance
upon and in conformity with written information furnished by such Holder
expressly for use in connection with such registration; and each such Holder
will pay, as incurred, any legal or other expenses reasonably incurred by any
person intended to be indemnified pursuant to this subsection 1.8(b), in
connection with investigating or defending any such loss, claim, damage,
liability, or action; provided, however, that the indemnity agreement contained
in this subsection 1.8(b) shall not apply to amounts paid in settlement of any
such loss, claim, damage, liability or action if such settlement is effected
without the consent of the Holder, which consent shall not be unreasonably
withheld; provided that in no event shall any indemnity under this subsection
1.8(b) exceed the net proceeds from the offering received by the Holder, unless
such liability arises out of or is based on the willful conduct of the Holder.

                           (c) Promptly after receipt by an indemnified party
under this Section 1.8 of notice of the commencement of any action (including
any governmental action), such indemnified party will, if a claim in respect
thereof is to be made against any indemnifying party under this Section 1.8,
deliver to the indemnifying party a written notice of the commencement thereof
and the indemnifying party shall have the right to participate in, and, to the
extent the indemnifying party so desires, jointly with any other indemnifying
party similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time of the
commencement of any such action, if prejudicial to its ability to defend such
action, shall relieve such indemnifying party of any liability to the
indemnified party under this Section 1.8, but the omission so to deliver written
notice to the indemnifying party will not relieve it of any liability that it
may have to any indemnified party otherwise than under this Section 1.8.

                           (d) If the indemnification provided in this Section
1.8 is held by a court of competent jurisdiction to be unavailable to an
indemnified party with respect to any loss, liability, claim, damage or expense
referred to therein, then the indemnifying party, in lieu of indemnifying such
indemnified party hereunder, shall contribute to the amount paid or payable by
such indemnified party as a result of such loss, liability, claim, damage or
expense in such proportion as is appropriate to reflect the relative fault of
the indemnifying party on the one hand and of the indemnified party on the other
in connection with the statements or omissions that resulted in such loss,
liability, claim, damage or expense as well as any other relevant equitable
considerations. The relative fault of the indemnifying party and of the
indemnified party shall be

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determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission to state a material fact
relates to information supplied by the indemnifying party or by the indemnified
party and the parties' relative intent, knowledge, access to information, and
opportunity to correct or prevent such statement or omission.

                           (e) The obligations of the Company and the Holder
under this Section 1.8 shall survive the completion of any offering of
Registrable Securities in a registration statement under this Section 1, and
otherwise.

                  1.9 REPORTS UNDER SECURITIES EXCHANGE ACT OF 1934. With a view
to making available to the Holder the benefits of Rule 144 promulgated under the
Securities Act and any other rule or regulation of the SEC that may at any time
permit the Holder to sell securities of the Company to the public without
registration, the Company agrees to use its best efforts to:

                           (a) make and keep public information available, as
those terms are understood and defined in SEC Rule 144, at all times;

                           (b) file with the SEC in a timely manner all reports
and other documents required of the Company under the Securities Act and the
Exchange Act; and

                           (c) furnish to the Holder, so long as the Holder owns
any Registrable Securities, forthwith upon request (i) a written statement by
the Company that it has complied with the reporting requirements of SEC Rule
144, the Securities Act and the Exchange Act, (ii) a copy of the most recent
annual or quarterly report of the Company and such other reports and documents
so filed by the Company, and (iii) such other information as may be reasonably
requested in availing the Holder of any rule or regulation of the SEC which
permits the selling of any such securities without registration.

                  1.10 ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause
the Company to register Registrable Securities pursuant to this Section 1 may be
assigned by a Holder to a transferee or assignee of all of the Holder's
Registrable Securities, provided the Company is, within a reasonable time after
such transfer, furnished with written notice of the name and address of such
transferee or assignee and the securities with respect to which such
registration rights are being assigned; and provided, further, that such
assignment shall be effective only if immediately following such transfer the
further disposition of such securities by the transferee or assignee is
restricted under the Securities Act.

                  1.11     EXPENSES OF REGISTRATION.

                           (a) DEMAND REGISTRATION. All expenses other than
underwriting discounts and commissions incurred in connection with
registrations, filings or qualifications pursuant to Section 1.2, including
(without limitation) all registration,

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filing and qualification fees, printers' and accounting fees, fees and
disbursements of counsel for the Company, and the reasonable fees and
disbursements of one counsel for the Holder shall be borne by the Company;
provided, however, that the Company shall not be required to pay for any
expenses of any registration proceeding begun pursuant to Section 1.2 if the
registration request is subsequently withdrawn at the request of the Holder,
unless, at the time of such withdrawal, the Holder has learned of a material
adverse change in the condition, business, or prospects of the Company from that
known to the Holder at the time of its request and has withdrawn the request
with reasonable promptness upon obtaining knowledge of such material adverse
change.

                           (b) COMPANY REGISTRATION. All expenses other than
underwriting discounts and commissions incurred in connection with
registrations, filings or qualifications of Registrable Securities pursuant to
Section 1.3 for the Holder, including (without limitation) all registration,
filing, and qualification fees, printers' and accounting fees, fees and
disbursements of counsel for the Company and the reasonable fees and
disbursements of one counsel for the Holder selected by it with the approval of
the Company, which approval shall not be unreasonably withheld, shall be borne
by the Company.

                  1.12 TERMINATION OF REGISTRATION RIGHTS. The rights granted
under this Section 1 shall terminate upon the earlier of (a) two years following
the date of this Agreement, or (b) at such time as the Holder may sell all of
its Registrable Securities in any single three month period pursuant to Rule 144
(or such successor rule as may be adopted).

         2.       MISCELLANEOUS.

                  2.1 AMENDMENTS AND WAIVERS. Any term of this Agreement may be
amended or waived with the written consent of the Company and the Holders of a
majority of the Shares then held by all Holders. Any amendment or waiver
effected in accordance with this Section 2.1 shall be binding upon the parties
and their respective successors and assigns.

                  2.2 SUCCESSORS AND ASSIGNS. Subject to the provisions of
Section 1.10, the terms and conditions of this Agreement shall inure to the
benefit of and be binding upon the respective successors and assigns of the
parties. Nothing in this Agreement, express or implied, is intended to confer
upon any party other than the parties hereto or their respective successors and
assigns any rights, remedies, obligations, or liabilities under or by reason of
this Agreement, except as expressly provided in this Agreement.

                  2.3 GOVERNING LAW. This Agreement and all acts and
transactions pursuant hereto and the rights and obligations of the parties
hereto shall be governed, construed and interpreted in accordance with the laws
of the State of New York, without giving effect to principles of conflicts of
law.

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                  2.4 COUNTERPARTS. This Agreement may be executed in two or
more counterparts, each of which shall be deemed an original and all of which
together shall constitute one instrument.

                  2.5 TITLES AND SUBTITLES. The titles and subtitles used in
this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

                  2.6 NOTICES. Any notice required or permitted by this
Agreement shall be in writing and shall be deemed sufficient upon receipt, when
delivered personally or by courier, overnight delivery service or confirmed
facsimile, or 48 hours after being deposited in the regular mail as certified or
registered mail (airmail if sent internationally) with postage prepaid, if such
notice is addressed to the party to be notified at such party's address or
facsimile number as set forth below (or as subsequently modified by written
notice):

         To the Holder:      Yahoo! Inc.
                             3420 Central Expressway
                             Santa Clara, CA 95051
                             Attn:  Senior Vice President, Corporate Development
                             Facsimile:  (408) 328-7939

                             With a copy at the same address to the
                             attention of the General Counsel, and a copy
                             to:

                             Venture Law Group
                             A Professional Corporation
                             2800 Sand Hill Road
                             Menlo Park, California 94025
                             Attn.:  Steven J. Tonsfeldt
                                     Keith A. Miller
                             Facsimile:  (415) 233-8386

         To the Company:     Net2Phone, Inc.
                             171 Main Street
                             Hackensack, New Jersey 07601
                             Attn:  Chief Executive Officer
                             Facsimile: (___) ____________

                             With a copy to:

                             Kirkland & Ellis
                             Aon Center
                             200 East Randolph Drive
                             Chicago, Illinois 60601

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<PAGE>   11
                             Attn:  Richard W. Porter
                             Facsimile:  (312) 861-2200

                  2.7 SEVERABILITY. If one or more provisions of this Agreement
are held to be unenforceable under applicable law, the parties agree to
renegotiate such provision in good faith, in order to maintain the economic
position enjoyed by each party as close as possible to that under the provision
rendered unenforceable. In the event that the parties cannot reach a mutually
agreeable and enforceable replacement for such provision, then (i) such
provision shall be excluded from this Agreement, (ii) the balance of the
Agreement shall be interpreted as if such provision were so excluded and (iii)
the balance of the Agreement shall be enforceable in accordance with its terms.

                  2.8 ENTIRE AGREEMENT. This Agreement is the product of all of
the parties hereto, and constitutes the entire agreement between such parties
pertaining to the subject matter hereof, and merges all prior negotiations and
drafts of the parties with regard to the transactions contemplated herein. Any
and all other written or oral agreements existing between the parties hereto
regarding such transactions are expressly canceled.

                  2.9 ADVICE OF LEGAL COUNSEL. Each party acknowledges and
represents that, in executing this Agreement, it has had the opportunity to seek
advice as to its legal rights from legal counsel and that the person signing on
its behalf has read and understood all of the terms and provisions of this
Agreement. This Agreement shall not be construed against any party by reason of
the drafting or preparation thereof.

                  2.10 DELAYS OR OMISSIONS. No delay or omission to exercise any
right, power or remedy accruing to any party to this Agreement, upon any breach
or default of the other party, shall impair any such right, power or remedy of
such non-breaching party nor shall it be construed to be a waiver of any such
breach or default, or an acquiescence therein, or of or in any similar breach or
default thereafter occurring; nor shall any waiver of any single breach or
default be deemed a waiver of any other breach or default theretofore or
thereafter occurring. Any waiver, permit, consent or approval of any kind or
character on the part of any party of any breach or default under this
Agreement, or any waiver on the part of any party of any provisions or
conditions of this Agreement, must be made in writing and shall be effective
only to the extent specifically set forth in such writing. All remedies, either
under this Agreement, or by law or otherwise afforded to any Holder, shall be
cumulative and not alternative.

                  2.11 THIRD PARTIES. Nothing in this Agreement, express or
implied, is intended to confer upon any party, other than the parties hereto,
and their respective successors and assigns, any rights, remedies, obligations
or liabilities under or by reason of this Agreement, except as expressly
provided herein.

                  2.12 PARITY OF RIGHTS. The registration rights granted to the
Holder under this Agreement are not intended by the parties to be senior to any
of the registration

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rights granted to holders of the Company's capital stock under that certain
Series A Preferred Shareholder Registration Rights Agreement dated as of May 13,
1999, but rather to rank on a pari passu basis with such rights. The parties
agree to interpret the terms of this Agreement in a manner consistent with the
foregoing intention.

                            [Signature Page Follows]

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         The parties have executed this Agreement as of the date first above
written.

                                         NET2PHONE, INC.

                                         By:    /s/ Howard Balter
                                         Title: Chief Executive Officer
                                         Address:      171 Main Street
                                                       Hackensack, NJ 07601

                                         YAHOO! INC.

                                         By:    /s/ Jeff Mallett
                                         Title: President and Chief
                                                Operating Officer
                                         Address:      3420 Central Expressway
                                                       Santa Clara, CA 95051<PAGE>   1
                                                                   EXHIBIT 10.49

                             ADIR TECHNOLOGIES, INC.

                         FORM OF FOUNDER STOCK AGREEMENT

         THIS AGREEMENT is made as of September 8, 2000, between Adir
Technologies, Inc., a Delaware corporation (the "Company"), and ________________
("Founder").

         The Company and Founder desire to enter into an agreement pursuant to
which Founder shall purchase, and the Company shall sell to Founder, _____
shares of the Company's common stock, par value $.01 per share, pursuant to the
Company's Stock Option and Incentive Plan, as amended from time to time. All of
such shares of common stock and all shares of common stock hereafter acquired by
Founder are referred to herein as "Founder Stock." Certain definitions are set
forth in paragraph 7 of this Agreement.

         The parties hereto agree as follows:

         1. PURCHASE AND SALE OF FOUNDER STOCK.

         (a) Upon execution of this Agreement, Founder shall irrevocably
purchase, and the Company shall sell to Founder, _____ (the "Shares") shares of
common stock at a price of $175.00 per share. The Company shall deliver to
Founder a copy of, and a receipt for, the certificate representing the Shares,
and Founder shall deliver to the Company a promissory note in the form of Annex
A attached hereto in the principal amount of $________ (the "Founder Note"), and
a check in the amount of $_____. Founder's obligations under the Founder Note
shall be secured by a pledge to the Company of all of the shares of Founder
Stock, and in connection therewith, Founder shall enter into a pledge agreement
in the form of Annex B attached hereto (the "Pledge Agreement").

         (b) The Company shall hold each certificate representing Founder Stock
until such time as the Founder Stock represented by such certificate is released
from the pledge to the Company and is fully vested hereunder.

         (c) Within 30 days after Founder purchases any Founder Stock from the
Company, Founder shall make an effective election with the Internal Revenue
Service under Section 83(b) of the Internal Revenue Code and the regulations
promulgated thereunder in the form of Annex C attached hereto.

         (d) In connection with the purchase and sale of the Founder Stock
hereunder, Founder represents and warrants to the Company that:

                  (i) The Founder Stock to be acquired by Founder pursuant to
         this Agreement shall be acquired for Founder's own account and not with
         a view to, or intention of, distribution thereof in violation of the
         1933 Act, or any applicable state securities laws,

                                      -1-
<PAGE>   2
         and the Founder Stock shall not be disposed of in contravention of the
         1933 Act or any applicable state securities laws.

                  (ii) Founder is an officer of Net2Phone, Inc. ("Net2Phone") or
         its Subsidiaries or their Affiliates, is sophisticated in financial
         matters and is able to evaluate the risks and benefits of the
         investment in the Founder Stock.

                  (iii) Founder is able to bear the economic risk of his
         investment in the Founder Stock for an indefinite period of time
         because the Founder Stock has not been registered under the 1933 Act
         and, therefore, cannot be sold unless subsequently registered under the
         1933 Act or an exemption from such registration is available.

                  (iv) Founder has had an opportunity to ask questions and
         receive answers concerning the terms and conditions of the offering of
         Founder Stock and has had full access to such other information
         concerning the Company as he has requested. Founder has reviewed, or
         has had an opportunity to review, a copy of that certain Assignment and
         License Agreement by and between the Company and Net2Phone.

                  (v) This Agreement constitutes the legal, valid and binding
         obligation of Founder, enforceable in accordance with its terms, and
         the execution, delivery and performance of this Agreement by Founder do
         not and shall not conflict with, violate or cause a breach of any
         agreement, contract or instrument to which Founder is a party or any
         judgment, order or decree to which Founder is subject.

         (e) As an inducement to the Company to issue the Founder Stock to
Founder, as a condition thereto, Founder acknowledges and agrees that:

                  (i) neither the issuance of the Founder Stock to Founder nor
         any provision contained herein shall entitle Founder to remain in the
         employment of Net2Phone and its Subsidiaries or their Affiliates or
         affect the right of Net2Phone and its Subsidiaries or their Affiliates
         to terminate Founder's employment at any time; and

                  (ii) the Company or Net2Phone shall have no duty or obligation
         to disclose to Founder, and Founder shall have no right to be advised
         of, any material information regarding Net2Phone and its Subsidiaries
         or their Affiliates at any time prior to, upon or in connection with
         the repurchase of Founder Stock upon the termination of Founder's
         employment with the Net2Phone and its Subsidiaries or their Affiliates
         or as otherwise provided hereunder.

         (f) The Company, Net2Phone and Founder acknowledge and agree that this
Agreement has been executed and delivered, and the Founder Stock has been issued
hereunder, in connection with and as a part of the compensation and incentive
arrangements between Net2Phone and its Subsidiaries and their Affiliates and
Founder.

                                      -2-
<PAGE>   3
         2. VESTING OF FOUNDER STOCK.

         (a) Except as otherwise provided in paragraph 2(b) below, the Founder
Stock shall become vested in accordance with the following schedule, if and only
if Founder has been continuously employed by Net2Phone or any of its
Subsidiaries or their Affiliates from the date hereof through and including the
date set forth below:

                  (i) 25% on the first anniversary of the date first written
above; and

                  (ii) 2.08% on the last day of each month for the thirty-six
months following the first anniversary of the date first written above.

         (b) In the event of a Corporate Transaction or Change in Control, all
shares of Founder Stock which have not yet become vested shall become vested at
the time of such event; provided, however, that any unvested Founder Stock shall
not automatically vest if such Founder Stock is, in connection with the
Corporate Transaction or Change in Control, exchanged for or converted into
comparable securities in the surviving or resulting corporation on terms and
conditions that substantially preserve the value, rights and benefits of the
Founder Stock then outstanding. In the event of the death or permanent
disability of Founder, the number of shares of Founder Stock which would have
become vested during the 12 months following Founder's death or the
determination of Founder's permanent disability (in addition to shares which
have already become vested) shall become vested as of the time of such death or
permanent disability. For purposes of this paragraph 2(b), the determination of
permanent disability shall be made in good faith by the Company's board of
directors (the "Board"). Shares of Founder Stock which have become vested are
referred to herein as "Vested Shares," and all other shares of Founder Stock are
referred to herein as "Unvested Shares."

         3. REPURCHASE OPTION.

         (a) In the event Founder ceases to be employed by Net2Phone and its
Subsidiaries or their Affiliates for any reason (the "Termination"), the
Unvested Shares (whether held by Founder or one or more of Founder's
transferees) shall be subject to repurchase by the Company and Net2Phone,
pursuant to the terms and conditions set forth in this paragraph 3 (the
"Repurchase Option").

         (b) The purchase price for each Unvested Share shall be Founder's
Original Cost for such share (with shares having the lowest cost subject to
repurchase prior to shares with a higher cost).

         (c) The Board may elect to purchase all or any portion of the Unvested
Shares by delivering written notice (the "Repurchase Notice") to the holder or
holders of the Founder Stock within 90 days after the Termination. The
Repurchase Notice shall set forth the number of Unvested Shares to be acquired
from each holder of Founder Stock, the aggregate consideration to be paid for
such shares and the time and place for the closing of the transaction. The
number of shares to be

                                      -3-
<PAGE>   4
repurchased by the Company shall first be satisfied to the extent possible from
the shares of Founder Stock held by Founder at the time of delivery of the
Repurchase Notice. If the number of shares of Founder Stock then held by Founder
is less than the total number of shares of Founder Stock the Company has elected
to purchase, the Company shall purchase the remaining shares elected to be
purchased from the other holder(s) of Founder Stock under this Agreement, pro
rata according to the number of shares of Founder Stock held by such other
holder(s) at the time of delivery of such Repurchase Notice (determined as close
as practicable to the nearest whole shares). The number of Unvested Shares to be
repurchased hereunder shall be allocated among Founder and the other holders of
Founder Stock (if any) pro rata according to the number of shares of Founder
Stock held by such persons.

         (d) If for any reason the Company does not elect to purchase all of the
Founder Stock pursuant to the Repurchase Option, Net2Phone shall be entitled to
exercise the Repurchase Option for the shares of Founder Stock the Company has
not elected to purchase (the "Available Shares"). As soon as practicable after
the Company has determined that there will be Available Shares, but in any event
within 45 days after the Termination, the Company shall give written notice (the
"Option Notice") to Net2Phone setting forth the number of Available Shares and
the purchase price for the Available Shares. Net2Phone may elect to purchase any
or all of the Available Shares by giving written notice to the Company within 30
days after the Option Notice has been given by the Company. As soon as
practicable, and in any event within ten days after the expiration of the 30-day
period set forth above, the Company shall notify each holder of Founder Stock as
to the number of shares being purchased from such holder by Net2Phone (the
"Supplemental Repurchase Notice"). At the time the Company delivers the
Supplemental Repurchase Notice to the holder(s) of Founder Stock, the Company
shall also deliver written notice to Net2Phone setting forth the number of
shares Net2Phone is entitled to purchase, the aggregate purchase price and the
time and place of the closing of the transaction.

         (e) The closing of the purchase of the Founder Stock pursuant to the
Repurchase Option shall take place on the date designated by the Company in the
Repurchase Notice or Supplemental Repurchase Notice, which date shall not be
more than 60 days nor less than five days after the delivery of the later of
either such notice to be delivered. The Company and/or Net2Phone shall pay for
the Founder Stock to be purchased pursuant to the Repurchase Option by delivery
of, in the case of Net2Phone, a check or wire transfer of funds and, in the case
of the Company at its option, (i) a check or wire transfer of funds, (ii) a
subordinated note or notes payable in up to three equal annual installments
beginning on the first anniversary of the closing of such purchase and bearing
interest (payable quarterly) at a rate per annum equal to the prime lending rate
charged by Money Center Banks as reported in the Wall Street Journal on the date
of issuance of such note or (iii) both (i) and (ii), in the aggregate amount of
the purchase price for such shares; provided that the Company shall use
reasonable efforts to make all such repurchases with a check or wire transfer of
funds. Any notes issued by the Company pursuant to this paragraph 3(e) shall be
subject to any restrictive covenants to which the Company is subject at the time
of such purchase. In addition, the Company may pay the purchase price for such
shares by offsetting amounts outstanding under the Founder Note issued to the
Company hereunder and under any other bona fide debts owed by Founder to the
Company. The purchasers of Founder Stock hereunder shall be entitled to receive

                                      -4-
<PAGE>   5
customary representations and warranties from the sellers regarding such sale of
shares (including representations and warranties regarding good title to such
shares, free and clear of any liens or encumbrances) and to require all sellers'
signatures be guaranteed by a nationally recognized bank or securities broker.

         (f) Notwithstanding anything to the contrary contained in this
Agreement, all repurchases of Founder Stock by the Company shall be subject to
applicable restrictions contained in the Delaware General Corporation Law and in
the Company's and its Subsidiaries debt and equity financing agreements. If any
such restrictions prohibit the repurchase of Founder Stock hereunder which the
Company is otherwise entitled or required to make, the time periods provided in
this paragraph 3 shall be suspended, and the Company may make such repurchases
as soon as it is permitted to do so under such restrictions.

         4. RESTRICTIONS ON TRANSFER. Founder shall not sell, transfer, assign,
pledge, or otherwise dispose of any interest in any shares of Founder Stock,
except pursuant to terms of that certain Right of First Offer and Co-Sale
Agreement of even date herewith, as amended and modified from time to time, a
form of which is attached hereto as Annex D. Any prospective transferee should
execute and deliver to the Company an instrument evidencing its agreement to be
bound to the provisions hereof.

         5. LEGEND. The certificates representing the Founder Stock shall bear
the following legend:

         "THE SECURITIES REPRESENTED BY THIS CERTIFICATE WERE ORIGINALLY ISSUED
         ON SEPTEMBER 8, 2000, HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT
         OF 1933, AS AMENDED (THE "ACT"), AND MAY NOT BE SOLD OR TRANSFERRED IN
         THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT OR AN
         EXEMPTION FROM REGISTRATION THEREUNDER. THE SECURITIES REPRESENTED BY
         THIS CERTIFICATE ARE ALSO SUBJECT TO ADDITIONAL RESTRICTIONS ON
         TRANSFER, CERTAIN REPURCHASE OPTIONS AND CERTAIN OTHER AGREEMENTS SET
         FORTH IN A FOUNDER STOCK AGREEMENT DATED AS OF SEPTEMBER 8, 2000, AND A
         RIGHT OF FIRST OFFER AND CO-SALE AGREEMENT DATED AS OF SEPTEMBER 8,
         2000, EACH AS AMENDED AND MODIFIED FROM TIME TO TIME. A COPY OF SUCH
         AGREEMENT MAY BE OBTAINED BY THE HOLDER HEREOF AT THE COMPANY'S
         PRINCIPAL PLACE OF BUSINESS WITHOUT CHARGE."

                                      -5-
<PAGE>   6
         6. SALE OF THE COMPANY.

         (a) If the Board and the holders of a majority of the Company's
Preferred Stock and common stock approve a Sale of the Company (the "Approved
Sale"), the holders of Founder Stock shall consent to and raise no objections
against the Approved Sale of the Company, and if the Approved Sale of the
Company is structured as a sale of stock, the holders of Founder Stock shall
agree to sell their shares of Founder Stock on the terms and conditions approved
by the Board and the holders of a majority of the Company's Preferred Stock and
common stock. The holders of Founder Stock shall take all necessary and
desirable actions in connection with the consummation of the Approved Sale of
the Company.

         (b) The obligations of the holders of Founder Stock with respect to the
Approved Sale of the Company are subject to the satisfaction of the condition
that upon the consummation of the Approved Sale, all of the holders of common
stock shall receive the same form and amount of consideration per share of
common stock, or if any holders of common stock are given an option as to the
form and amount of consideration to be received, all holders shall be given the
same option.

         (c) If the Company or the holders of the Company's securities enter
into any negotiation or transaction for which Rule 506 (or any similar rule then
in effect) promulgated by the Securities Exchange Commission may be available
with respect to such negotiation or transaction (including a merger,
consolidation or other reorganization), the holders of Founder Stock shall at
the request of the Company, appoint a "purchaser representative" (as such term
is defined in Rule 501) reasonably acceptable to the Company. If any holder of
Founder Stock appoints a purchaser representative designated by the Company, the
Company shall pay the fees of such purchaser representative. However, if any
holder of Founder Stock declines to appoint the purchaser representative
designated by the Company, such holder shall appoint another purchaser
representative (reasonably acceptable to the Company), and such holder shall be
responsible for the fees of the purchaser representative so appointed.

         (d) Founder and the other holders of Founder Stock (if any) shall bear
their pro-rata share (based upon the number of shares sold) of the costs of any
sale of Founder Stock pursuant to an Approved Sale to the extent such costs are
incurred for the benefit of all holders of common stock and are not otherwise
paid by the Company or the acquiring party. Costs incurred by Founder and the
other holders of Founder Stock on their own behalf shall not be considered costs
of the transaction hereunder.

         (e) The provisions of this paragraph 6 shall terminate upon the
completion of a Qualified Public Offering, Sale of the Company, Corporate
Transaction or Change in Control.

         7. DEFINITIONS.

         "Affiliate" of any particular Person means any other Person
controlling, controlled by or under common control with such particular Person,
where "control" means the possession,

                                      -6-
<PAGE>   7
directly or indirectly, of the power to direct the management and policies of a
Person whether through the ownership of voting securities, contract or
otherwise.

         "Corporate Transaction" shall have the same meaning as set forth in the
Company's 2000 Stock Option and Incentive Plan.

         "Change in Control" shall have the same meaning as set forth in the
Company's 2000 Stock Option and Incentive Plan.

         "Founder Stock" shall continue to be Founder Stock in the hands of any
holder other than Founder (except for the Company and Net2Phone and except for
transferees in a Public Sale), and except as otherwise provided herein, each
such other holder of Founder Stock shall succeed to all rights and obligations
attributable to Founder as a holder of Founder Stock hereunder. Founder Stock
shall also include shares of the Company's capital stock issued with respect to
Founder Stock by way of a stock split, stock dividend or other recapitalization.
Notwithstanding the foregoing, all Vested and Unvested Shares shall remain
Founder Stock after any Transfer thereof.

         "Independent Third Party" means any person who, immediately prior to
the contemplated transaction, does not own in excess of 5% of the Company's
common stock on a fully-diluted basis, who is not controlling, controlled by or
under common control with any such 5% owner of the Company's common stock and
who is not the spouse or descendent (by birth or adoption) of any such 5% owner
of the Company's common stock.

         "1933 Act" means the Securities Act of 1933, as amended from time to
time.

         "Original Cost" of each share of common stock purchased hereunder shall
be equal to $175.00 (as proportionately adjusted for all subsequent stock
splits, stock dividends and other recapitalizations).

         "Qualified Public Offering" means the sale, in an underwritten public
offering registered under the 1933 Act, of shares of the Company's common stock
having an aggregate offering value of at least $20 million and a per share price
of at least three times Original Cost.

         "Person" means an individual, a partnership, a corporation, a limited
liability company, an association, a joint stock company, a trust, a joint
venture, an unincorporated organization and a governmental entity or any
department, agency or political subdivision thereof.

         "Preferred Stock" means any class or series of capital stock of the
Company which is designated preferred stock.

         "Public Sale" means any sale pursuant to a registered public offering
under the 1933 Act or any sale to the public pursuant to Rule 144 promulgated
under the 1933 Act effected through a broker, dealer or market maker.

                                      -7-
<PAGE>   8
         "Sale of the Company" means the sale of the Company to an Independent
Third Party or affiliated group of Independent Third Parties pursuant to which
such party or parties acquire (i) capital stock of the Company possessing the
voting power to elect a majority of the Company's board of directors (whether by
merger, consolidation or sale or transfer of the Company's capital stock) or
(ii) all or substantially all of the Company's assets determined on a
consolidated basis.

         "Subsidiary" means any corporation of which Net2Phone owns securities
having a majority of the ordinary voting power in electing the board of
directors directly or through one or more subsidiaries.

         8. NOTICES. Any notice provided for in this Agreement must be in
writing and must be either personally delivered, mailed by first class mail
(postage prepaid and return receipt requested) or sent by reputable overnight
courier service (charges prepaid) to the recipient at the address below
indicated:

             To the Company:                  Adir Technologies, Inc.
                                              520 Broad Street
                                              Newark, NJ 07102
                                              Fax: (973) ___-_____
                                              Attn:  President

             With copies to (which will
             not constitute notice):          Kirkland & Ellis
                                              200 E. Randolph Dr.
                                              Chicago, IL 60601
                                              Fax: (312) 861-2200
                                              Attn: Richard W. Porter, Esq.

             To Founder:                      __________________
                                              Net2Phone, Inc.
                                              520 Broad Street
                                              Newark, NJ 07102
                                              Fax:  (973) ___-____

             To Net2Phone:                    Net2Phone, Inc.
                                              520 Broad Street
                                              Newark, NJ 07102
                                              Fax: (973) 412-3800
                                              Attn: General Counsel

or such other address or to the attention of such other person as the recipient
party shall have specified by prior written notice to the sending party. Any
notice under this Agreement shall be

                                      -8-
<PAGE>   9
deemed to have been given when so delivered or sent or, if mailed, five days
after deposit in the U.S. mail.

         9. GENERAL PROVISIONS.

         (a) Transfers in Violation of Agreement. Any Transfer or attempted
Transfer of any Founder Stock in violation of any provision of this Agreement
shall be void, and the Company shall not record such Transfer on its books or
treat any purported transferee of such Founder Stock as the owner of such stock
for any purpose.

         (b) Severability. Whenever possible, each provision of this Agreement
shall be interpreted in such manner as to be effective and valid under
applicable law, but if any provision of this Agreement is held to be invalid,
illegal or unenforceable in any respect under any applicable law or rule in any
jurisdiction, such invalidity, illegality or unenforceability shall not affect
any other provision or any other jurisdiction, but this Agreement shall be
reformed, construed and enforced in such jurisdiction as if such invalid,
illegal or unenforceable provision had never been contained herein.

         (c) Complete Agreement. This Agreement, those documents expressly
referred to herein and other documents of even date herewith embody the complete
agreement and understanding among the parties and supersede and preempt any
prior understandings, agreements or representations by or among the parties,
written or oral, which may have related to the subject matter hereof in any way.

         (d) Counterparts. This Agreement may be executed in separate
counterparts, each of which is deemed to be an original and all of which taken
together constitute one and the same agreement.

         (e) Successors and Assigns. Except as otherwise provided herein, this
Agreement shall bind and inure to the benefit of and be enforceable by Founder,
the Company, Net2Phone and their respective successors and assigns (including
subsequent holders of Founder Stock); provided that the rights and obligations
of Founder under this Agreement shall not be assignable except in connection
with a permitted transfer of Founder Stock hereunder.

         (f) Choice of Law. The corporate law of the State of Delaware shall
govern all questions concerning the relative rights of the Company and its
stockholders. All other questions concerning the construction, validity,
enforcement and interpretation of this Agreement and the exhibits hereto shall
be governed by the internal law, and not the law of conflicts, of the State of
New Jersey.

         (g) Remedies. Each of the parties to this Agreement (including the
Founders) shall be entitled to enforce its rights under this Agreement
specifically, to recover damages and costs (including reasonable attorney's
fees) caused by any breach of any provision of this Agreement and to exercise
all other rights existing in its favor. The parties hereto agree and acknowledge
that

                                      -9-
<PAGE>   10
money damages would not be an adequate remedy for any breach of the provisions
of this Agreement and that any party may in its sole discretion apply to any
court of law or equity of competent jurisdiction (without posting any bond or
deposit) for specific performance and/or other injunctive relief in order to
enforce or prevent any violations of the provisions of this Agreement.

         (h) Amendment and Waiver. The provisions of this Agreement may be
amended and waived only with the prior written consent of the Company, Founder
and Net2Phone.

         (i) Third-Party Beneficiaries. Certain provisions of this Agreement are
entered into for the benefit of and shall be enforceable by Net2Phone as
provided herein.

         (j) Business Days. If any time period for giving notice or taking
action hereunder expires on a day which is a Saturday, Sunday or legal holiday
in the state in which the Company's chief Founder office is located, the time
period shall be automatically extended to the business day immediately following
such Saturday, Sunday or holiday.

                                 *  *  *  *

                                      -10-
<PAGE>   11
         IN WITNESS WHEREOF, the parties hereto have executed this Agreement on
the date first written above.

                                            ADIR TECHNOLOGIES, INC.

                                            ____________________________________
                                            By: ________________________________
                                            Its: _______________________________

                                            ____________________________________

                                      -11-

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