Document:

<PAGE>
                                                                     Exhibit 4.3

                                 NET2PHONE, INC.
                             STOCK OPTION AGREEMENT

     This STOCK OPTION AGREEMENT is entered into on August 6, 2001 by and
between Net2Phone, Inc., a Delaware corporation (the "Company"), and Eric
Constantini (the "Employee").

     WHEREAS, the Company desires to grant to the Employee options not subject
to any Stock Option Plan of the Company to acquire an aggregate of 50,000 shares
of common stock of the Company, par value $.01 per share (the "Stock"), on the
terms set forth herein.

     NOW, THEREFORE, the parties hereby agree as follows:

     1. Grant of Options. The Employee is hereby granted stock options (the
        ----------------
"Options") to purchase an aggregate of 50,000 shares of Stock, pursuant to the
terms of this Agreement.

     2. Term. The Options may be exercised in whole or in part until 5:00 p.m.
        ----
Eastern Standard Time, on January 3, 2005 (the "Option Term").

     3. Option Price. The initial exercise price per share of the Options shall
        ------------
be $4.36, subject to adjustment as provided elsewhere herein.

     4. Conditions to Exercisability. The Options shall become vested
        ----------------------------
immediately upon execution of this Agreement and shall be exercisable thereafter
until the end of the Option Term, whether or not the Employee continues to be in
the employ of, or maintains any relationship with the Company. The terms and
conditions in paragraphs 6(e), 13, 16(b), 18, 19 and 20 of Company's 1999
Amended and Restated Stock Option and Incentive Plan ("Plan") as amended on
November 6, 2000, including all relevant definitions set forth in the Plan, are
hereby incorporated by reference in this Agreement, subject to paragraphs 7 and
13 hereof.

     5. Withholding Taxes. As a condition of the exercise of an Option, no later
        -----------------
than the date of exercise of the Option ("Tax Event"), the Employee will pay to
the Company or make arrangements satisfactory to the Company regarding payment
of any U.S. federal, state or local taxes of any kind required by such law to be
withheld at such time, provided that Employee is subject to such taxes.
Alternatively, solely to the extent required by U.S. law or otherwise agreed to
by the Employee, the Company may deduct the amount of any U.S. federal, state or
local taxes of any kind required by law to be so withheld upon the Tax Event
from any payment of any kind due to the Employee. The withholding obligation may
be satisfied by the withholding or delivery of Stock, but solely at the request
of the Employee.

     6. Registration of Company Stock. Not later than November 1, 2001, the
        -------------------------------------------------------------------
Company will file a registration statement with the Securities and Exchange
---------------------------------------------------------------------------
Commission on such authorized form as is appropriate with respect to the Shares
-------------------------------------------------------------------------------
which are the subject
---------------------

                                        1

<PAGE>

of the Options and, at its sole cost and expense, will keep such registration
------------------------------------------------------------------------------
statement effective and current until the earlier of (i) Employees's exercise of
--------------------------------------------------------------------------------
all Options granted hereunder or (ii) January 3, 2005.
-----------------------------------------------------

     7.  Entire Agreement. This Agreement contains all of the understandings
     --------------------
between the parties hereto pertaining to the matters referred to herein, and
supersedes all undertakings and agreements, whether oral or in writing,
previously entered into by them with respect thereto, except the Settlement
Agreement bearing even date herewith between the Company and the Employee and
others ("Settlement Agreement"). The Employee represents that, in executing this
Agreement, he does not rely upon and has not relied upon any representation or
statement not set forth herein or in the Settlement Agreement made by the
Company with regard to the subject matter of this Agreement or otherwise.

     8.  Amendment or Modification, Waiver. No provision of this Agreement may
     -------------------------------------
be amended or waived unless such amendment or waiver is agreed to in writing,
signed by the Employee and by a duly authorized officer of the Company. No
waiver by any party hereto of any breach by another party hereto of any
condition or provision of this Agreement to be performed by such other party
shall be deemed a waiver of a similar of dissimilar condition or provision at
the same time, any prior time or any subsequent time.

     9.  Effect of Certain Changes.
     -----------------------------

         (a) In the event of any extraordinary dividend, stock dividend
(including a spin off or split off of a Subsidiary of the Company, as defined in
the Plan), recapitalization, merger, consolidation, stock split, warrants or
rights issuance, or combination or exchange of such shares, the number of shares
of Stock covered by this grant and/or the price per share of the Options shall
be equitably adjusted, in each such case so as to reflect such event and
preserve the value of the Options herein granted; provided however, that any
fractional shares resulting from such adjustment shall be eliminated.

         (b) In the event of a change in the Stock of the Company as presently
constituted that is limited to a change of all of its authorized shares of
common stock into the same number of shares with a different par value or
without par value, the shares resulting from any such change shall be deemed to
be Stock within the meaning of this agreement.

     10. Notices. Each notice relating to this Agreement shall be in writing and
         -------
delivered in person or by certified mail to the proper address. All notices to
the Company shall be addressed to it at:

         Net2Phone, Inc.
         520 Broad Street, 12/th/ Floor
         Newark, New Jersey 07102

         Attn: Human Resources

                                        2

<PAGE>

All notices to the Employee or other person or persons then entitled to exercise
the Options shall be addressed to the Employee or such other person or persons
at:

          Eric Constantini
          -------------------------
          65 Avenue Niel
          -------------------------
          75017 Paris, France
          -------------------------

Anyone to whom a notice may be given under this Agreement may designate a new
address by notice to such effect.

     11.  Severability. If any provision of this Agreement or the application of
     -----------------
any such provision to any party or circumstances shall be determined by any
court of competent jurisdiction to be invalid and unenforceable to any extent,
the remainder of this Agreement or the application of such provision to such
person or circumstances other than those to which it is so determined to be
invalid and unenforceable, shall not be affected thereby, and each provision
hereof shall be validated and shall be enforced to the fullest extent permitted
by law.

     12.  Governing Law. This Agreement shall be construed and governed in
     ------------------
accordance with the laws of the state of Delaware, without regard to principles
of conflicts of laws.

     13.  Headings. All descriptive headings of sections and paragraphs in this
     -------------
Agreement are intended solely for convenience, and no provision of this
Agreement is to be construed by reference to the heading of any section or
paragraph.

     14.  Construction. This Agreement is made under and subject to the
     -----------------
provisions of the Settlement Agreement. If there is a conflict between any
provision of this Agreement and the Settlement Agreement then the Settlement
Agreement shall prevail.

     15.  Counterparts. This Agreement may be executed in counterparts, each of
     -----------------
which shall be deemed to be an original but both of which together shall
constitute one and the same instrument.

IN WITNESS WHEREOF, the Company has caused this Agreement to be executed by an
authorized officer and the Employee has hereunto set his hand all as of the date
first above written.

                                               NET2PHONE, INC.

                                               By: ____________________________
                                                   Name:
                                                   Title:

                                               Employee:
                                               Name:___________________________
                                               Title:__________________________

                                        3<PAGE>
                                                                    EXHIBIT 10.7

                                 AMENDMENT NO. 3
                                     TO THE
                          REGISTRATION RIGHTS AGREEMENT

     Reference is made to that certain Registration Rights Agreement (the
"Agreement") entered into as of July 20, 2001, by and among MetaSolv, Inc., a
Delaware corporation (the "Company"), each of the persons identified on Exhibit
A attached thereto (together with each assignee pursuant to Section 6(c)
thereof, collectively the "Shareholders") and Joseph Hatchuel, acting as the
representative for each Shareholder thereunder (the "Shareholders'
Representative"). This Amendment No. 3 to the Registration Rights Agreement
(this "Amendment") is entered into as of November 16, 2001, by and between the
Company and the Shareholders' Representative.

                                    RECITALS:
                                    --------

     A. The Company and the Shareholders' Representative entered into Amendment
No. 1 to the Registration Rights Agreement as of August 3, 2001 and Amendment
No. 2 to the Registration Rights Agreement as of August 10, 2001 (together, the
"Previous Amendments").

     B. The Company and the Shareholders' Representative, acting on behalf of
each Shareholder, wish to enter into this Amendment to amend the Agreement as
provided herein.

     C. Pursuant to those certain Powers of Attorney executed by each
Shareholder of various dates falling in June and July 2001, each Shareholder has
authorized the Shareholders' Representative to execute, deliver and perform this
Amendment on such Shareholder's behalf.

     NOW, THEREFORE, for valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto agree as follows:

                                   AGREEMENTS:
                                   ----------

     1. The parties hereto agree that Section 3(a) of the Agreement shall be
amended and restated in its entirety to read as follows:

          "(a) Shareholder Obligations. From and after the declared effective
               -----------------------
     date of the Registration Statement, each Shareholder proposing to sell any
     Registrable Securities pursuant thereto shall notify the Company in writing
     (a "Sale Notice") of such Shareholder's intent to sell Registrable
     Securities. The Company may, in its discretion, notify such Shareholder
     (the "Company Notice") within three Business Days following the receipt by
     the Company of a Sale Notice that such Shareholder shall, pursuant to
     Section 3(d), discontinue disposition of such Registrable Securities. If
     the Company fails to provide the Company Notice within three Business Days
     following the receipt by the Company of such Sale Notice, then such
     Shareholder shall have the right to dispose of such Registrable Securities
     for a period of thirty days following the

                                       1

<PAGE>

     date of receipt of the Company Notice (the "Sale Period"). After the
     expiration of such Sale Period such Shareholder shall be required to
     provide the Company with an additional Sale Notice in order to sell
     Registrable Securities. Each Shareholder's rights under this Section 3(a)
     are subject in all respects to the Company's rights and the Shareholders'
     duties under Section 3(d)."

     2. The parties hereto agree that Section 3(d) of the Agreement shall be
amended such that all references in Section 3(d) to "subsection 3(a)(iii)" shall
be replaced with references to "subsection 3(b)(iii)."

     3. The parties hereto agree that, except as set forth above in paragraphs 1
and 2 and except as provided in the Previous Amendments, the Agreement shall
remain unaffected and in full force and effect.

     4. THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF DELAWARE, WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OR
CHOICE OF LAW.

               [THE REMAINDER OF THIS PAGE IS INTENTIONALLY BLANK]

                                       2

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of
the date first above written.

                                      METASOLV, INC.

                                      By: /s/ Jonathan K. Hustis
                                          --------------------------------------
                                      Name:   Jonathan K. Hustis
                                            ------------------------------------
                                      Title:  Vice President - Business Services
                                             -----------------------------------

                                      SHAREHOLDERS' REPRESENTATIVE:

                                      /s/ Joseph Hatchuel
                                      ------------------------------------------
                                      Joseph Hatchuel

                                       3

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00034-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00034-of-00352.parquet"}]]