<PAGE>


                                                                    Exhibit 10.7

                              SONUS NETWORKS, INC.

                            SERIES D PREFERRED STOCK
                               PURCHASE AGREEMENT






                                  March 9, 2000






<PAGE>


                              SONUS NETWORKS, INC.

                            SERIES D PREFERRED STOCK
                               PURCHASE AGREEMENT

                                TABLE OF CONTENTS
                                -----------------

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                                                                                                     PAGE
                                                                                                     ----
<S>     <C>                                                                                          <C>
1.       Authorization and Sale of Shares............................................................ 1
         1.1      Authorization...................................................................... 1
         1.2      Sale of Shares..................................................................... 1
         1.3      Use of Proceeds.................................................................... 1

2.       The Closing................................................................................. 1

3.       Representations of the Company.............................................................. 2
         3.1      Organization and Standing.......................................................... 3
         3.2      Capitalization..................................................................... 4
         3.3      Subsidiaries, Etc.................................................................. 4
         3.4      Issuance of Shares; Agreements..................................................... 4
         3.5      Authority for Agreement............................................................ 4
         3.6      Governmental Consents.............................................................. 5
         3.7      Litigation......................................................................... 5
         3.8      Financial Statements............................................................... 5
         3.9      Absence of Certain Changes......................................................... 5
         3.10     Taxes.............................................................................. 6
         3.11     Title to Properties................................................................ 6
         3.12     Leasehold Interests................................................................ 6
         3.13     Intellectual Property.............................................................. 7
         3.14     Material Contracts and Obligations................................................. 8
         3.15     Compliance......................................................................... 8
         3.16     Employees.......................................................................... 9
         3.17     ERISA.............................................................................. 9
         3.18     Books and Records..................................................................10
         3.19     U.S. Real Property Holding Corporation.............................................10
         3.20     Disclosures........................................................................10
         3.21     Year 2000 Compatibility............................................................10

4.       Representations of the Purchasers...........................................................11
         4.1      Investment.........................................................................11
         4.2      Authority..........................................................................11
         4.3      Experience.........................................................................11
         4.4      Status.............................................................................12


<PAGE>


5.       Covenants of the Company....................................................................12
         5.1      Inspection.........................................................................12
         5.2      Financial Statements and Other Information.........................................12
         5.3      Material Changes and Litigation....................................................13
         5.4      Insurance..........................................................................13
         5.5      Employee Agreements................................................................14
         5.6      Related Party Transactions.........................................................14
         5.7      Reservation of Common Stock........................................................14
         5.8      Board of Directors.................................................................14
         5.9      Termination of Covenants...........................................................14

6.       Transfer of Shares..........................................................................15
         6.1      Restricted Shares..................................................................15
         6.2      Requirements for Transfer..........................................................15
         6.3      Legend.............................................................................16
         6.4      Rule 144A Information..............................................................16

7.       Miscellaneous...............................................................................16
         7.1      Successors and Assigns.............................................................16
         7.2      Confidentiality....................................................................16
         7.3      Survival of Representations and Warranties.........................................17
         7.4      Expenses...........................................................................17
         7.5      Notices............................................................................17
         7.6      Brokers............................................................................17
         7.7      Entire Agreement...................................................................17
         7.8      Amendments and Waivers.............................................................18
         7.9      Counterparts.......................................................................18
         7.10     Section Headings...................................................................18
         7.11     Severability.......................................................................18
         7.12     Governing Law......................................................................18

         Schedule I
         Disclosure Schedule

         Exhibit A  Form of Restated Certificate
         Exhibit B  Form of Opinion of Bingham Dana LLP
         Exhibit C  Form of Investor Agreement
         Exhibit D  Form of Right of First Refusal Agreement
         Exhibit E  Form of Stock Repurchase Agreement
         Exhibit F  Form of Noncompetition and Confidentiality Agreement
</TABLE>



<PAGE>


                   SERIES D PREFERRED STOCK PURCHASE AGREEMENT
                   -------------------------------------------

         This Series D Preferred Stock Purchase Agreement (this "AGREEMENT"),
dated as of March 9, 2000, is entered into by and among Sonus Networks, Inc., a
Delaware corporation (the "COMPANY"), and the persons and entities listed on
SCHEDULE I attached hereto (individually, a "PURCHASER" and, collectively, the
"PURCHASERS").

         In consideration of the mutual promises and covenants contained in this
Agreement, the parties hereto agree as follows:

         1.       AUTHORIZATION AND SALE OF SHARES.

                  1.1 AUTHORIZATION. The Company has duly authorized the sale
and issuance, pursuant to the terms of this Agreement, of up to 1,585,366 shares
of its Series D Convertible Preferred Stock, $0.01 par value per share (the
"SERIES D PREFERRED STOCK"), having the rights, restrictions, privileges and
preferences set forth in the Third Amended and Restated Certificate of
Incorporation of the Company attached hereto as EXHIBIT A (the "RESTATED
CERTIFICATE"). The Company has adopted and filed the Restated Certificate with
the Secretary of State of the State of Delaware.

                  1.2 SALE OF SHARES. Subject to the terms and conditions of
this Agreement the Company will issue and sell to each Purchaser, and each
Purchaser will purchase, for a purchase price of $16.40 per share, such number
of shares of Series D Preferred Stock as is set forth opposite such Purchaser's
name on SCHEDULE I attached hereto. The shares of Series D Preferred Stock being
sold under this Agreement are referred to as the "SHARES." The Company's
agreement with each of the Purchasers is a separate agreement, and the sale of
Shares to each of the Purchasers is a separate sale.

                  1.3 USE OF PROCEEDS. The Company will use the proceeds from
the sale of the Shares for working capital purposes, the purchase of fixed
assets, the acquisition of other businesses and/or technologies and the
repayment of certain indebtedness.

         2. THE CLOSING. (a) The closing (the "CLOSING") of the sale and
purchase of the Shares under this Agreement shall take place at the offices of
Bingham Dana LLP, 150 Federal Street, Boston, Massachusetts at 9:00 a.m. on the
date of this Agreement, or at such other time, date and place as are mutually
agreeable to the Company and the Purchasers. The date of the Closing is
hereinafter referred to as the "CLOSING DATE."

            (b) At the Closing:


<PAGE>


                                      -2-


                (i) the Company shall deliver to the Purchasers a certificate,
as of the most recent practicable date, as to the corporate good standing of the
Company issued by the Secretary of State of the State of Delaware;

                (ii) the Company shall deliver to the Purchasers the Restated
Certificate of Incorporation, as in effect as of the Closing Date, certified by
the Secretary of State of the State of Delaware;

                (iii) the Company shall deliver to the Purchasers a
Certificate of the Secretary of the Company attesting to (i) the By-laws of
the Company, and (ii) resolutions of the Board of Directors and the
stockholders of the Company authorizing and approving all matters in
connection with this Agreement and the transactions contemplated hereby;

                (iv) Bingham Dana LLP, counsel for the Company, shall deliver to
the Purchasers an opinion, dated the Closing Date, in the form attached hereto
as EXHIBIT B;

                (v) the Company and the Purchasers shall execute and deliver the
Third Amended and Restated Investor Rights Agreement in the form attached hereto
as EXHIBIT C (the "INVESTOR AGREEMENT");

                (vi) the Company, the Purchasers and the other parties thereto
shall execute and deliver the Third Amended and Restated Right of First Refusal
and Co-Sale Agreement in the form attached hereto as EXHIBIT D (the "RIGHT OF
FIRST REFUSAL AGREEMENT");

                (vii) the Company shall deliver to each Purchaser a copy of a
waiver of the pre-emptive rights of the holders of Series A, Series B and Series
C Preferred Stock;

                (viii) the Company shall deliver to each Purchaser a certificate
for the number of Shares being purchased by such Purchaser, registered in the
name of such Purchaser;

                (ix) each Purchaser shall pay to the Company the purchase price
for the Shares being purchased by such Purchaser, by wire transfer or certified
check; and

                (x) the Company and each of the Purchasers shall execute and
deliver a cross-receipt.

         3. REPRESENTATIONS OF THE COMPANY. The Company hereby represents and
warrants to the Purchasers as follows, subject in each case to such exceptions
as are


<PAGE>


                                      -3-


specifically contemplated by this Agreement or as are set forth in the
Disclosure Schedule attached hereto (the "DISCLOSURE SCHEDULE"). Notwithstanding
any other provision of this Agreement or the Disclosure Schedule, each exception
set forth in the Disclosure Schedule will be deemed to qualify each
representation and warranty set forth in this Agreement that is specifically
identified (by cross-reference or otherwise) in the Disclosure Schedule as being
qualified by such exception.

            3.1 ORGANIZATION AND STANDING. The Company is a corporation
duly organized, validly existing and in good standing under the laws of the
State of Delaware and has full corporate power and authority to conduct its
business as presently conducted and as proposed to be conducted by it and to
enter into and perform this Agreement and to carry out the transactions
contemplated by this Agreement. The Company is duly qualified to do business as
a foreign corporation and is in good standing in the Commonwealth of
Massachusetts and in any other jurisdiction in which the failure to so qualify
would have a material adverse effect on the operations or financial condition of
the Company. The Company has furnished to special counsel to the Purchasers true
and complete copies of its Restated Certificate and By-laws, each as amended to
date and presently in effect.

            3.2 CAPITALIZATION. The authorized capital stock of the Company
(immediately prior to the Closing) consists of (a) 17,000,000 shares of
preferred stock, $0.01 par value per share (of which 7,220,000 shares have been
designated as Series A Convertible Preferred Stock (the "SERIES A PREFERRED
STOCK"), 3,247,857 shares have been designated as Series B Convertible Preferred
Stock (the "SERIES B PREFERRED STOCK"), 2,153,072 shares have been designated as
Series C Convertible Preferred Stock (the "SERIES C PREFERRED STOCk"), and
1,585,366 have been designated as Series D Convertible Preferred Stock, of which
7,180,000 shares of Series A Preferred Stock, 3,204,287 shares of Series B
Preferred Stock, 1,939,681 shares of Series C Preferred Stock, and no shares of
Series D Preferred Stock are issued or outstanding and (b) 70,000,000 shares of
common stock, $0.001 par value per share (the "COMMON Stock"), of which (i)
8,292,731 shares are issued and outstanding other than those under the Company's
Amended and Restated 1997 Stock Incentive Plan (as amended, the "PLAN"), (ii)
16,250,000 shares have been reserved for issuance pursuant to the Plan, of which
the Company has issued or committed to issue not more than an aggregate of
15,759,922 shares in the form of restricted shares of Common Stock or stock
options exercised or exercisable for shares of Common Stock pursuant to the
terms of such Plan, and (iii) 30,809,920 shares have been reserved for issuance
upon the conversion of the Shares, shares of Series A Preferred Stock, shares of
Series B Preferred Stock, and shares of Series C Preferred Stock. At the
Closing, the Common Stock, the Series A Preferred Stock, the Series B Preferred
Stock, the Series C Preferred Stock and the Series D Preferred Stock will have
the voting powers, designations, preferences, rights and qualifications, and
limitations or restrictions set forth in the Restated Certificate. All of the
issued and outstanding shares of Common Stock have been duly authorized and
validly issued and are fully paid and nonassessable. Except for the Series A
Preferred Stock, the Series B Preferred Stock or the Series C


<PAGE>


                                      -4-


Preferred Stock or as set forth in Section 3.2 of the Disclosure Schedule or as
contemplated by this Agreement, (i) no subscription, warrant, option,
convertible security or other right (contingent or otherwise) to purchase or
acquire any shares of capital stock of the Company is authorized or outstanding,
(ii) the Company has no obligation (contingent or otherwise) to issue any
subscription, warrant, option, convertible security or other such right or to
issue or distribute to holders of any shares of its capital stock any evidences
of indebtedness or assets of the Company, and (iii) the Company has no
obligation (contingent or otherwise) to purchase, redeem or otherwise acquire
any shares of its capital stock or any interest therein or to pay any dividend
or make any other distribution in respect thereof. All of the issued and
outstanding shares of capital stock of the Company have been offered, issued and
sold by the Company in compliance in all material respects with applicable
Federal and state securities laws.

            3.3 SUBSIDIARIES, ETC. Except as set forth in Section 3.3 of the
Disclosure Schedule, the Company has no subsidiaries and does not own or
control, directly or indirectly, any shares of capital stock of any other
corporation or any interest in any partnership, joint venture or other
non-corporate business enterprise.

            3.4 ISSUANCE OF SHARES; AGREEMENTS. The issuance, sale and
delivery of the Shares in accordance with this Agreement, and the issuance and
delivery of the shares of Common Stock issuable upon conversion of the Shares,
have been duly authorized by all necessary corporate action on the part of the
Company, and all such shares have been duly reserved for issuance. The Shares
when so issued, sold and delivered against payment therefor in accordance with
the provisions of this Agreement, and the shares of Common Stock issuable upon
conversion of the Shares, when issued upon such conversion, will be duly and
validly issued, fully paid and non-assessable. Except as set forth in Section
3.4 of the Disclosure Schedule or as contemplated by this Agreement, there are
no agreements, written or oral, between the Company and any holder of its
capital stock, or, to the best of the Company's knowledge, among any holders of
its capital stock, relating to the acquisition (including without limitation
rights of first refusal or pre-emptive rights), disposition, registration under
the Securities Act of 1933, as amended (the "SECURITIES ACT"), or voting of the
capital stock of the Company.

            3.5 AUTHORITY FOR AGREEMENT. The execution, delivery and performance
by the Company of this Agreement and all other agreements required to be
executed by the Company at the Closing pursuant to Section 2 (the "ANCILLARY
AGREEMENTS"), and the consummation by the Company of the transactions
contemplated hereby and thereby, have been duly authorized by all necessary
corporate action. This Agreement and the Ancillary Agreements have been, or as
of the Closing will have been, duly executed and delivered by the Company and
constitute, or as of the Closing will constitute, valid and binding obligations
of the Company enforceable in accordance with their respective terms. The
execution of and performance of the transactions contemplated by this Agreement
and the Ancillary Agreements and compliance with their provisions by the Company
will not violate any provision of applicable law and will not


<PAGE>


                                      -5-


conflict with or result in any breach of any of the terms, conditions or
provisions of, or constitute a default under, or require a consent or waiver
under, its Restated Certificate or By-laws (each as amended to date) or any
material indenture, lease, agreement or other instrument to which the Company is
a party or by which it or any of its properties is bound, or any decree,
judgment, order, statute, rule or regulation applicable to the Company which
would have a material adverse effect on the business, properties or results of
operations of the Company (a "MATERIAL ADVERSE EFFECT").

            3.6 GOVERNMENTAL CONSENTS. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any governmental authority is required on the part of the Company
in connection with the execution and delivery of this Agreement, the offer,
issuance, sale and delivery of the Shares, or the other transactions to be
consummated at the Closing, as contemplated by this Agreement, other than such
filings as shall have been made prior to and shall be effective on and as of the
Closing. Based on the representations made by the Purchasers in Section 4 of
this Agreement, the offer and sale of the Shares to the Purchasers will be
exempt from the registration requirements of applicable Federal and state
securities laws.

            3.7 LITIGATION. Except as set forth in Section 3.7 of Disclosure
Schedule, there is no action, suit or proceeding, or governmental inquiry or
investigation, pending, or, to the best of the Company's knowledge, any basis
therefor or threat thereof, against the Company, which questions the validity of
this Agreement or the right of the Company to enter into it, or which might
result, either individually or in the aggregate, in any material adverse change
in the business, assets or condition, financial or otherwise, of the Company,
nor is there any litigation pending, or, to the best of the Company's knowledge,
any basis therefor or threat thereof, against the Company by reason of the
activities of the Company, or negotiations by the Company with possible
investors in the Company.

            3.8 FINANCIAL STATEMENTS. The Company has delivered to the
Purchasers copies of (i) its unaudited balance sheet as of December 31, 1999,
and the related unaudited statements of operations, redeemable convertible
preferred stock and stockholders' deficit, and cash flows for the fiscal year
then ended and for the period from inception (August 7, 1997) to December 31,
1999, and (ii) its unaudited balance sheet as of January 31, 2000 (the "MOST
RECENT BALANCE SHEET"), and the related unaudited statements of operations,
redeemable convertible stock and stockholders' deficit, and cash flows for the
one (1) month period then ended and for the period from inception (August 7,
1997) to January 31, 2000 (the "INTERIM FINANCIALS"). Except as set forth in
Section 3.8 of the Disclosure Schedule, each of such balance sheets fairly
presents, in all material respects, the financial condition of the Company as of
its respective date, and each of such statements of operations, redeemable
convertible preferred stock and stockholders' deficit, and cash flows fairly
presents, in all material respects, the results of operations, redeemable
convertible preferred stock and stockholders' deficit, or cash flows, as the
case may be, of the Company for the period


<PAGE>


                                      -6-


covered thereby; in each case in accordance with generally accepted accounting
principles, subject to the absence of footnotes and normal year-end adjustments.

            3.9 ABSENCE OF CERTAIN CHANGES. Except as set forth in Section
3.9 of the Disclosure Schedule, since the date of the Most Recent Balance Sheet,
there have not been any changes in the business, assets, financial condition, or
operating results of the Company that, either individually or in the aggregate,
have had a Material Adverse Effect (as defined in Section 3.5 hereof).

            3.10 TAXES. The Company has filed all tax returns required to
be filed by it on or prior to the date hereof, each such tax return has been
prepared in compliance with all applicable laws and regulations, and, to the
best of the Company's knowledge, all such tax returns are true and accurate in
all material respects. All taxes due and payable by the Company with respect to
any periods ending on or before the Closing Date have been paid. No claim has
ever been made by a taxing authority in a jurisdiction where the Company does
not pay tax or file tax returns that the Company is or may be subject to taxes
assessed by such jurisdiction. There are no liens for taxes (other than current
taxes not yet due and payable) on the assets of the Company. No action, suit,
taxing authority proceeding, or audit with respect to any tax is pending or, to
the best of the Company's knowledge, threatened, against or with respect to the
Company. No deficiency or proposed adjustment in respect of taxes that has not
been settled or otherwise resolved has been asserted or assessed by any taxing
authority against the Company. The Company has withheld and paid all taxes
required to have been withheld and paid by it in connection with amounts paid or
owing to any employee, creditor, independent contractor, or other person.
Neither the Company nor any of its stockholders has ever filed (a) an election
pursuant to Section 1362 of the Internal Revenue Code of 1986, as amended (the
"CODE"), that the Company be taxed as an S Corporation, or (b) consent pursuant
to Section 341(f) of the Code relating to collapsible corporations.

            3.11 TITLE TO PROPERTIES. Except as set forth in Section 3.11
of the Disclosure Schedule, the Company has good and valid title to its
properties and assets reflected in the Most Recent Balance Sheet or acquired by
it since the date of the Most Recent Balance Sheet (other than properties and
assets disposed of in the ordinary course of business since the date of the Most
Recent Balance Sheet), and, except as set forth in Section 3.11 of the
Disclosure Schedule, all such properties and assets are free and clear of
mortgages, pledges, security interests, liens, charges, claims, restrictions and
other encumbrances (including without limitation, easements and licenses),
except for liens for current taxes not yet due and payable and minor
imperfections of title, if any, not material in nature or amount and not
materially detracting from the value or impairing the use of the property
subject thereto or impairing the ability or operations of the Company, including
without limitation, the ability of the Company to secure financing using such
properties and assets as collateral. To the best of the Company's knowledge,
there are no condemnation, environmental, zoning or other land use regulation
proceedings, either instituted or planned to be instituted, which would
adversely affect the use or operation of


<PAGE>


                                      -7-


the Company's properties and assets for their intended uses and purposes, or the
value of such properties, and the Company has not received notice of any special
assessment proceedings which would affect such properties and assets.

            3.12 LEASEHOLD INTERESTS. Each lease or agreement to which the
Company is a party under which it is a lessee of any property, real or personal,
is a valid and subsisting agreement, duly authorized and entered into by the
Company, without any default of the Company thereunder and, to the best of the
Company's knowledge, without any default thereunder of any other party thereto.
No event has occurred and is continuing which, with due notice of lapse of time
or both, would constitute a default or event of default by the Company under any
such lease or agreement or, to the best of the Company's knowledge, by any other
party thereto. The Company's possession of such property has not been disturbed
and, to the best of the Company's knowledge, no claim has been asserted against
the Company adverse to its rights in such leasehold interests.

            3.13 INTELLECTUAL PROPERTY.

                 (a) To the best of the Company's knowledge, except as set forth
in Section 3.13(a) of the Disclosure Schedule, no third party has claimed or has
reason to claim that any person employed by or affiliated with the Company, in
connection with his or her employment by or affiliation with the Company, (i)
has violated or is violating any of the terms or conditions of his or her
employment, non-competition or non-disclosure agreement with such third party,
(ii) has disclosed or is disclosing or has utilized or is utilizing any trade
secret or proprietary information or documentation of such third party or (iii)
has interfered or is interfering in the employment relationship between such
third party and any of its present or former employees. Except as set forth in
Section 3.13(a) of the Disclosure Schedule, no third party has requested
information from the Company which suggests that such a claim might be
contemplated. To the best of the Company's knowledge, no person employed by or
affiliated with the Company has employed or proposes to employ any trade secret
or any information or documentation proprietary to any former employer, and to
the best of the Company's knowledge, no person employed by or affiliated with
the Company has violated any confidential relationship which such person may
have had with any third party, in connection with the development, manufacture
or sale or any product or proposed product or the development or sale of any
service or proposed service of the Company, and the Company has no reason to
believe there will be any such employment or violation. To the best of the
Company's knowledge, none of the execution or delivery of this Agreement, or the
carrying on of business of the Company by any officer, director or key employee
of the Company, or the conduct or proposed conduct of the business of the
Company, will conflict with or result in a breach of the terms, conditions or
provisions of or constitute a default under any contract, covenant or instrument
under which any such person is obligated which would have a Material Adverse
Effect.


<PAGE>


                                      -8-


                 (b) Set forth in Section 3.13(b) of the Disclosure Schedule is
a list of all domestic and foreign patents, patent rights, patent applications,
trademarks, trademark applications, service marks, service mark applications,
trade names and copyrights, and all applications for such which are currently in
the process of being prepared, owned by or registered in the name of the
Company, or of which the Company is a licensor or licensee or in which the
Company has any right, and in each case a brief description of the nature of
such right. Except as set forth in Section 3.13(b) of the Disclosure Schedule,
the Company owns or possesses adequate licenses or other rights to use all
patents, patent applications, trademarks, trademark applications, service marks,
service mark applications, trade names, copyrights, manufacturing processes,
formulae, trade secrets, customer lists and know-how (collectively,
"INTELLECTUAL PROPERTY") necessary for the conduct of its business as conducted
and as proposed to be conducted. Except as otherwise provided in Section 3.13(b)
of the Disclosure Schedule, no claim is pending or, to the best of the Company's
knowledge, threatened to the effect that the operations of the Company infringe
upon or conflict with the asserted rights of any other person under any
Intellectual Property, and, to the best of the Company's knowledge, there is no
basis for any such claim (whether or not pending or threatened). No claim is
pending or, to the best of the knowledge of the Company, threatened to the
effect that any such Intellectual Property owned or licensed by the Company, or
which the Company otherwise has the right to use, is invalid or unenforceable by
the Company, and, to the best of the Company's knowledge, there is no basis for
any such claim (whether or not pending or threatened). To the best of the
Company's knowledge, all technical information developed by and belonging to the
Company which has not been patented has been kept confidential. Except as set
forth in Section 3.13(b) of the Disclosure Schedule, the Company has not granted
or assigned to any other person or entity any right to manufacture, have
manufactured, assemble or sell the products or proposed products or to provide
the services or proposed services of the Company.

            3.14 MATERIAL CONTRACTS AND OBLIGATIONS. Except as contemplated by
this Agreement or as listed in Section 3.14 of the Disclosure Schedule, the
Company is not a party to any material agreement or commitment of any nature,
including without limitation (a) any agreement which requires future
expenditures by the Company in excess of $100,000, (b) any employment or
consulting agreement, employee benefit, bonus, pension, profit-sharing, stock
option, stock purchase or similar plan or arrangement, or distributor or sales
representative agreement, (c) any agreement with any stockholder, officer or
director of the Company, or any "affiliate" or "associate" of such persons (as
such terms are defined in the rules and regulations promulgated under the
Securities Act), including without limitation any agreement or other arrangement
providing for the furnishing of services by, rental of real or personal property
from, or otherwise requiring payments to, any such person or entity or (d) any
agreement relating to the intellectual property rights of the Company.

            3.15 COMPLIANCE. Except as set forth in Section 3.15 of the
Disclosure Schedule, the Company has, to its knowledge, in all material
respects, complied with all


<PAGE>


                                      -9-


laws, regulations and orders applicable to its present and proposed business and
has all material permits and governmental licenses required thereby. There is no
term or provision of any mortgage, indenture, contract, agreement or instrument
to which the Company is a party or by which it is bound, or, to the best of the
Company's knowledge, of any provision of any state or Federal judgment, decree,
order, statute, rule or regulation applicable to or binding upon the Company,
which materially adversely affects or, so far as the Company may now foresee, in
the future is reasonably likely to materially adversely affect, the business,
assets or condition, financial or otherwise, of the Company. Except as set forth
in Section 3.15 of the Disclosure Schedule, to the best of the Company's
knowledge, no employee of the Company is in violation of any term of any
contract or covenant (either with the Company or with another entity) relating
to employment, patents, proprietary information disclosure, non-competition or
non-solicitation.

            3.16 EMPLOYEES.

                 (a) Each holder of Common Stock has executed and delivered to
the Company a Stock Repurchase Agreement in substantially the form attached
hereto as EXHIBIT E, and all of such agreements are in full force and effect.

                 (b) Each employee of the Company has executed and delivered to
the Company a Noncompetition and Confidentiality Agreement covering a period of
one year following the termination of such employee's employment with the
Company, in substantially the form attached hereto as EXHIBIT F, and all of such
agreements are in full force and effect.

                 (c) None of the employees of the Company is represented by any
labor union, and there is no labor strike or other labor trouble pending with
respect to the Company (including, without limitation, any organizational drive)
or, to the best of the Company's knowledge, threatened.

            3.17 ERISA.

                 (a) Except as set forth on SCHEDULE 3.17 hereto, the Company
does not maintain and has no obligation to make contributions to, any employee
benefit plan (an "ERISA PLAN") within the meaning of Section 3(3) of the United
States Employee Retirement Income Security Act of 1974, as amended ("ERISA"), or
any other retirement, profit sharing, stock option, stock bonus or employee
benefit plan (a "NON-ERISA PLAN"). All such ERISA Plans and Non-ERISA Plans have
been maintained and operated in all material respects in accordance with all
federal, state and local laws applicable to such plans, and the terms and
conditions of the respective plan documents, except where the failure to so
maintain or operate such ERISA Plans and Non-ERISA Plans would not have a
Material Adverse Effect.


<PAGE>


                                      -10-


                 (b) No material liability to the United States Pension Benefit
Guaranty Corporation ("PBGC"), or to any multi-employer pension plan within the
meaning of section 3(35) of ERISA, or to any other governmental authority,
pension or retirement board, or other agency, under any federal, state or local
law, has been or is expected to be incurred by the Company with respect to any
ERISA or Non-ERISA Plan. There has been no "reportable event" within the meaning
of Section 4043(b) of ERISA with respect to any ERISA Plan, and no event or
condition that presents a material risk of termination of any ERISA Plan by the
PBGC.

                 (c) Full payment has been made of all material amounts that the
Company is required under the terms of each ERISA Plan and Non-ERISA Plan, or
pursuant to applicable federal, state or local law, to have paid as
contributions to such ERISA Plan or Non-ERISA Plan as of the last day of the
most recent fiscal year of such ERISA Plan or Non-ERISA Plan ended prior to the
date hereof, and no accumulated funding deficiency (as defined in Section 302 of
ERISA and Section 412 of the Code), whether or not waived, exists with respect
to any ERISA Plan.

            3.18 BOOKS AND RECORDS. The minute books of the Company contain
records of all meetings and other corporate actions of its stockholders and its
Board of Directors and committees thereof, which are complete and accurate in
all material respects. The stock ledger of the Company is complete and reflects
all issuances, transfers, repurchases and cancellations of shares of capital
stock of the Company.

            3.19 U.S. REAL PROPERTY HOLDING CORPORATION. The Company is not now
and has never been a "United States Real Property Holding Corporation" as
defined in Section 897(c)(2) of the Code and Section 1.897-2(b) of the
Regulations promulgated by the Internal Revenue Service.

            3.20 DISCLOSURES. Neither this Agreement nor any Schedule or Exhibit
hereto, nor any certificate or instrument furnished to the Purchasers at the
Closing or as required by the terms of this Agreement, when read together,
contains or will contain any untrue statement of a material fact or omits or
will omit to state a material fact necessary in order to make the statements
contained herein or therein, in light of the circumstances under which they were
made, not misleading.

            3.21 YEAR 2000 COMPATIBILITY. To the best of the Company's
knowledge, all of the Company's material products (including products currently
under development), if applicable, will record, store, process and calculate and
present calendar dates falling on and after January 1, 2000, and will calculate
any information dependent on or relating to such dates in substantially the same
manner and with substantially the same functionality, data integrity and
performance as the products record, store, process, calculate and present
calendar dates on or before December 31, 1999, or calculate any information
dependent on or relating to such date (collectively "Year 2000 Compliant"). To
the best of the Company's knowledge, all of the Company's material products will
lose


<PAGE>


                                      -11-


no material functionality with respect to the introduction of records containing
dates falling on or after January 1, 2000. To the best of the Company's
knowledge, all of the Company's internal computer systems, including without
limitation, its accounting systems, are Year 2000 Compliant.

         4. REPRESENTATIONS OF THE PURCHASERS. Each Purchaser represents and
warrants to the Company as follows:

            4.1 INVESTMENT. Such Purchaser is acquiring the Shares, and the
shares of Common Stock into which the Shares may be converted, for its or his
own account for investment and not with a view to, or for sale in connection
with, any distribution thereof, nor with any present intention of distributing
or selling the same; and such Purchaser has no present or contemplated
agreement, undertaking, arrangement, obligation, indebtedness or commitment
providing for the disposition thereof. Such Purchaser acknowledges that the
Shares are restricted securities as defined under the Securities Act and shall
bear the legends set forth in Section 6.3 hereof.

            4.2 AUTHORITY. Such Purchaser has full power and authority to
enter into and to perform this Agreement in accordance with its terms. Such
Purchaser represents that it has not been organized, reorganized or
recapitalized specifically for the purpose of investing in the Company. This
Agreement and the Ancillary Agreement to be executed by such Purchaser have been
duly executed and delivered by such Purchaser and constitute valid and binding
obligations of such Purchaser enforceable in accordance with their respective
terms. The execution of and performance of the transactions contemplated by this
Agreement and the Ancillary Agreements to be executed by such Purchaser and
compliance with their provisions by such Purchaser will not violate any
provision of law and will not conflict with or result in any breach of any of
the terms, conditions or provisions of, or constitute a default under, or
require a consent or waiver under, its organizational documents (each as amended
to date) or any indenture, lease, agreement or other instrument to which the
Purchaser is a party or by which it or any of its properties is bound, or any
decree, judgment, order, statute, rule or regulation applicable to such
Purchaser.

            4.3 EXPERIENCE. Such Purchaser has carefully reviewed the
representations concerning the Company contained in this Agreement and has made
detailed inquiry concerning the Company, its business and its personnel; the
officers of the Company have made available to such Purchaser any and all
written information which it has requested and have answered to such Purchaser's
satisfaction all inquiries made by such Purchaser; and such Purchaser has
sufficient knowledge and experience in investing in companies similar to the
Company so as to be able to evaluate the risks and merits of its investment in
the Company and is able financially to bear the risks thereof, including a
complete loss of its investment. Such Purchaser understands that an investment
in the Company involves a high degree of risk in view of the fact that the


<PAGE>


                                      -12-


Company is a start-up enterprise with minimal operating history, and there may
never be an established market for the Company's capital stock.

            4.4 STATUS. Such Purchaser is an "accredited investor" as that
term is defined in Rule 501 of Regulation D promulgated under the Securities
Act. Such Purchaser represents that its investment in Series D Preferred Stock
will not violate any existing policy of its employer and that it has the
authority to make such an investment.

         5. COVENANTS OF THE COMPANY.

            5.1 INSPECTION. The Company shall permit each Purchaser (together
with any of its affiliates) holding not less than 237,805 shares of Series D
Stock at the relevant time (as adjusted for stock splits, stock dividends,
recapitalizations and similar events), or any authorized representative thereof,
to visit and inspect the properties of the Company, including its corporate and
financial records, and to discuss its business and finances with officers of the
Company, during normal business hours following reasonable notice and as often
as may be reasonably requested, without interruption of the business of the
Company and subject to the confidentiality obligations of Section 7.2 hereof.

            5.2  FINANCIAL STATEMENTS AND OTHER INFORMATION.

                 (a) So long as a Purchaser (together with any of its
affiliates) holds at least 237,805 shares of Series D Preferred Stock (as
adjusted for stock splits, stock dividends, recapitalizations and similar
events), the Company shall deliver to such Purchaser:

                     (i) within 90 days after the end of each fiscal year of the
Company, an audited balance sheet of the Company as at the end of such year, and
audited statements of operations, stockholders' equity and cash flows of the
Company for such year, certified by certified public accountants of established
national reputation selected by the Company, and prepared in accordance with
generally accepted accounting principles; and

                     (ii) within 45 days after the end of each fiscal quarter of
the Company, an unaudited balance sheet of the Company as at the end of such
quarter, and unaudited statements of operations and cash flows of the Company
for such fiscal quarter and for the current fiscal year to the end of such
fiscal quarter.

                 (b) So long as a Purchaser (together with any of its
affiliates) holds at least 237,805 shares of Series D Preferred Stock (as
adjusted for stock splits, stock dividends, recapitalizations and similar
events), the Company shall deliver to such Purchaser:


<PAGE>


                                      -13-


                     (i) within 30 days after the end of each month, an
unaudited balance sheet of the Company as at the end of such month and unaudited
statements of operations and cash flows of the Company for such month and for
the current fiscal year to the end of such month, setting forth in comparative
form the Company's projected financial statements for the corresponding periods
for the current fiscal year;

                     (ii) as soon as  available, but in any event within 30 days
after commencement of each new fiscal year, a budget, consisting of projected
financial statements for such fiscal year; and

                     (iii) with reasonable promptness, such other notices,
information and data with respect to the Company as the Company delivers to the
holders of its Common Stock, and such other information and data as such
Purchaser may from time to time reasonably request.

                 (c) The foregoing financial statements shall be prepared on a
consolidated basis if the Company then has any subsidiaries. The financial
statements delivered pursuant to clause (ii) of paragraph (a) and clause (i) of
paragraph (b) shall be accompanied by a certificate of the chief financial
officer of the Company stating that such statements have been prepared in
accordance with generally accepted accounting principles consistently applied
(except as noted) and fairly present, in all material respects, the financial
condition and results of operations of the Company at the date thereof and for
the periods covered thereby (subject, in the case of any such unaudited
financial statements to the absence of footnotes and to year-end adjustments).

            5.3  MATERIAL CHANGES AND LITIGATION. The Company shall promptly
notify the Purchasers of any material adverse change in the business, assets or
condition, financial or otherwise, of the Company and of any litigation or
governmental proceeding or investigation brought or, to the best of the
Company's knowledge, threatened against the Company, or against Hassan Ahmed,
Rubin Gruber, Michael G. Hluchyj or Kwok P. Wong (the "FOUNDERS") or any
officer, director, key employee or principal stockholder of the Company
materially adversely affecting or which, if adversely determined, would
materially adversely affect the Company's business, prospects, assets or
condition, financial or otherwise.

            5.4  INSURANCE.

                 (a) The Company shall maintain for a period of at least three
years from the procurement thereof, term life insurance upon the lives of each
of the Founders, in the amount of $1,000,000, with the proceeds payable to the
Company.

                 (b) The Company shall maintain in effect, policies of workers'
compensation insurance and of insurance with respect to its properties and
business,


<PAGE>


                                      -14-


including, without limitation, insurance against loss, damage, fire, theft,
public liability and other risks, which is adequate for the maintenance and
preservation of the Company's properties and business.

            5.5  EMPLOYEE AGREEMENTS. The Company shall require all employees
hereafter employed or engaged by the Company who are at or above the director
level or other key employees to enter into a Noncompetition and Confidentiality
Agreement covering a period of one year following the termination of such
employee's employment with the Company, substantially in the form attached
hereto as EXHIBIT F or in such other form as may be approved by the Board of
Directors.

            5.6  RELATED PARTY TRANSACTIONS. The Company shall not enter into
any agreement with any stockholder, officer or director of the Company, or any
"affiliate" or "associate" of such persons (as such terms are defined in the
rules and regulations promulgated under the Securities Act), including without
limitation any agreement or other arrangement providing for the furnishing of
services by, rental of real or personal property from, or otherwise requiring
payments to, any such person or entity, without the consent of at least a
majority of the members of the Company's Board of Directors having no interest
in such agreement or arrangement.

            5.7  RESERVATION OF COMMON STOCK. The Company shall reserve and
maintain a sufficient number of shares of Common Stock for issuance upon
conversion of all of the outstanding Shares.

            5.8 TERMINATION OF COVENANTS. The covenants of the Company contained
in Sections 5.1 through 5.7 shall terminate, and be of no further force or
effect, upon the closing of the Company's first offering of Common Stock to the
public, resulting in net proceeds to the Company of at least $25,000,000, and at
a price per share of at least $19.68 (as adjusted for stock splits, stock
dividends, recapitalizations and similar events) or, at such time as the
Purchasers (together with any affiliated entities to whom Shares have been
transferred) own less than an aggregate of 237,805 shares of Series D Preferred
Stock (as adjusted for stock splits, stock dividends, recapitalizations and
similar events).

            5.9 QUALIFIED SMALL BUSINESS STOCK. The Company shall submit to its
stockholders (including the Purchasers) and to the Internal Revenue Service any
reports that may be required under Section 1202(d)(1)(C) of the Code and the
Regulations promulgated thereunder. In addition, within ten days after a
Purchaser's written request therefor, the Company shall deliver to such
Purchaser a written statement indicating whether such Purchaser's interest in
the Company constitutes "qualified small business stock" as defined in Section
1202(c) of the Code.


<PAGE>


                                      -15-


         6. TRANSFER OF SHARES.

            6.1  RESTRICTED SHARES. "RESTRICTED SHARES" means (i) the Shares,
(ii) the shares of Common Stock issued or issuable upon conversion of the
Shares, (iii) any shares of capital stock of the Company acquired by a Purchaser
pursuant to the Investor Agreement or the Right of First Refusal Agreement, and
(iv) any other shares of capital stock of the Company issued in respect of such
shares (as a result of stock splits, stock dividends, reclassifications,
recapitalizations, or similar events); PROVIDED, HOWEVER, that shares of Common
Stock which are Restricted Shares shall cease to be Restricted Shares (i) upon
any sale pursuant to a registration statement under the Securities Act, or under
Section 4(1) of the Securities Act or Rule 144 under the Securities Act, or (ii)
at such time as they become eligible for sale under Rule 144(k) under the
Securities Act.

            6.2  REQUIREMENTS FOR TRANSFER.

                 (a) Restricted Shares shall not be sold or transferred unless
(1) either (i) they first shall have been registered under the Securities Act,
or (ii) the Company first shall have been furnished with an opinion of legal
counsel, reasonably satisfactory to the Company, to the effect that such sale or
transfer is exempt from the registration requirements of the Securities Act and
(2) such actions are in compliance with applicable state securities laws.

                 (b) Notwithstanding the foregoing, no registration or opinion
of counsel shall be required for (i) a transfer by a Purchaser which is a
partnership to a partner of such partnership or a retired partner of such
partnership who retires after the date hereof, or to the estate of any such
partner or retired partner, if the transferee agrees in writing to be subject to
the terms of this Section 6 to the same extent as if he were an original
Purchaser hereunder, or (ii) a transfer made in accordance with Rule 144 under
the Securities Act.

            6.3  LEGEND. Each certificate representing Restricted Shares shall
bear a legend substantially in the following form:

         "The shares represented by this certificate have not been registered
         under the Securities Act of 1933, as amended, and may not be offered,
         sold or otherwise transferred, pledged or hypothecated unless and until
         such shares are registered under such Act or an opinion of counsel
         satisfactory to the Company is obtained to the effect that such
         registration is not required."

         The foregoing legend shall be removed from the certificates
representing any Restricted Shares, at the request of the holder thereof, at
such time as they become eligible for resale pursuant to Rule 144(k) under the
Securities Act.


<PAGE>


                                      -16-


            6.4  RULE 144A INFORMATION. The Company shall, at all times
during which it is neither subject to the reporting requirements of Section 13
or 15(d) of the Securities Exchange Act of 1934, as amended (the "EXCHANGE
ACT"), nor exempt from reporting pursuant to Rule 12g3-2(b) under the Exchange
Act, upon the written request of a Purchaser, provide in writing to such
Purchaser, and to any prospective transferee of any Restricted Shares of such
Purchaser, the information concerning the Company described in Rule 144A(d)(4)
under the Securities Act ("RULE 144A INFORMATION"). The Company also shall, upon
the written request of a Purchaser, cooperate with and assist such Purchaser or
any member of the National Association of Securities Dealers, Inc. PORTAL system
in applying to designate and thereafter maintain the eligibility of the
Restricted Shares for trading through PORTAL. The Company's obligations under
this Section 6.4 shall at all times be contingent upon receipt from the
prospective transferee of Restricted Shares of a written agreement to take all
reasonable precautions to safeguard the Rule 144A Information from disclosure to
anyone other than persons who will assist such transferee in evaluating the
purchase of any Restricted Shares and to use such Rule 144A Information only for
such evaluation purposes.

         7. MISCELLANEOUS.

            7.1  SUCCESSORS AND ASSIGNS. This Agreement, and the rights and
obligations of each Purchaser hereunder, may be assigned by such Purchaser to
any person or entity to which at least 237,805 Shares, as adjusted for stock
splits, stock dividends, recapitalizations and similar events (or 100% of the
Shares originally purchased hereunder by such Purchaser, if less than 237,805
Shares), are transferred by such Purchaser, and such transferee shall be deemed
a "Purchaser" for purposes of this Agreement; provided that the transferee
provides written notice of such assignment to the Company and agrees to be bound
by the terms and conditions set forth herein.

            7.2  CONFIDENTIALITY. The Purchasers agree that they will keep
confidential and will not disclose or divulge any confidential, proprietary or
secret information which they may obtain from the Company pursuant to financial
statements, reports and other materials submitted by the Company to the
Purchasers pursuant to this Agreement or any rights granted hereunder, unless
such information is known, or until such information becomes known, to the
public; PROVIDED, HOWEVER, that a Purchaser may disclose such information (i) to
its attorneys, accountants, consultants, and other professionals to the extent
necessary to obtain their services in connection with its investment in the
Company, (ii) to any prospective purchaser of any Shares from such Purchaser as
long as such prospective purchaser agrees in writing to be bound by the
provisions of this Section, or (iii) to any affiliate of such Purchaser or to a
partner, shareholder or subsidiary of such Purchaser; subject to the agreement
of such party to keep such information confidential as set forth herein. Each
Purchaser agrees that it will not make, issue or release any public
announcement, public statement or public acknowledgement of the dollar amount of
any Purchaser's investment in Series D Preferred Stock. In addition, no
Purchaser shall make, issue or release any public


<PAGE>


                                      -17-


announcement, public statement or public acknowledgement of who served as the
lead investor in the Series D Preferred Stock financing unless the lead investor
shall have reviewed such release prior to its publication.

            7.3 SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All agreements,
representations and warranties contained herein shall survive the execution and
delivery of this Agreement and the closing of the transactions contemplated
hereby for a period of eighteen (18) months from the date hereof.

            7.4 EXPENSES. The Company shall pay, at the Closing, the reasonable
costs and expenses of Gibson, Dunn & Crutcher LLP, counsel to the Purchasers,
not to exceed $15,000 in the aggregate, in connection with the preparation of
this Agreement and the other agreements and documents contemplated hereby and
the closing of the transactions contemplated hereby.

            7.5 NOTICES. All notices, requests, consents, and other
communications under this Agreement shall be in writing and shall be delivered
by hand, sent via a reputable nationwide overnight courier service or mailed by
first class certified or registered mail, return receipt requested, postage
prepaid:

         If to the Company, at Sonus Networks, Inc., 5 Carlisle Road, Westford,
MA 01886, Attn: President, or at such other address or addresses as may have
been furnished in writing by the Company to the Purchasers, with a copy to
Bingham Dana LLP, 150 Federal Street, Boston, MA 02110, Attn: David L. Engel,
Esq.

         If to a Purchaser, at its address as set forth on SCHEDULE I attached
hereto, or at such other address or addresses as may have been furnished to the
Company in writing by such Purchaser, with a copy to Gibson, Dunn & Crutcher
LLP, Attn: Peter Heilmann, Esq.

         Notices provided in accordance with this Section 7.5 shall be deemed
delivered upon personal delivery, one business day after being sent via a
reputable nationwide overnight courier service, or five business days after
deposit in the mail.

            7.6 BROKERS. The Company and the Purchasers each (i) represents and
warrants to the other parties hereto that he, she or it has retained no finder
or broker in connection with the transactions contemplated by this Agreement,
and (ii) will indemnify and save the other parties harmless from and against any
and all claims, liabilities or obligations with respect to brokerage or finders'
fees or commissions in connection with the transactions contemplated by this
Agreement asserted by any person on the basis of any agreement, statement or
representation alleged to have been made by such indemnifying party.


<PAGE>


                                      -18-


            7.7 ENTIRE AGREEMENT. This Agreement and the Ancillary Agreements
embody the entire agreement and understanding between the parties hereto with
respect to the subject matter hereof and supersedes all prior agreements and
understandings relating to such subject matter.

            7.8 AMENDMENTS AND WAIVERS. Except as otherwise expressly set
forth in this Agreement, any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a
particular instance and either retroactively or prospectively), with the written
consent of the Company and the holders of at least 66 2/3% of the shares of
Common Stock issued or issuable upon conversion of the Shares. Any amendment or
waiver effected in accordance with this Section 7.8 shall be binding upon each
holder of any Shares (including shares of Common Stock into which such Shares
have been converted) and each future holder of all such securities and the
Company. No waivers of or exceptions to any term, condition or provision of this
Agreement, in any one or more instances, shall be deemed to be, or construed as,
a further or continuing waiver of any such term, condition or provision.

            7.9 COUNTERPARTS. 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 be one and the same document.

            7.10 SECTION HEADINGS. The section headings are for the convenience
of the parties and in no way alter, modify, amend, limit, or restrict the
contractual obligations of the parties.

            7.11 SEVERABILITY. The invalidity or unenforceability of any
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement.

            7.12 GOVERNING LAW. This Agreement shall be governed by and
construed in accordance with the laws of the State of Delaware.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


<PAGE>


         Executed as an instrument under seal as of the date first written
above.

         COMPANY:

         SONUS NETWORKS, INC.



         By: /s/ Hassan Ahmed
            ------------------------------
                  Hassan Ahmed
                  President


         PURCHASERS:


         BroadBand Office, Inc.
         2900 Telestar Court
         Falls Church, VA  22042

              By: /s/ Johnson Agogbua
                 ------------------------------
                  Name: Johnson Agogbua
                  Title: Vice President, Engineering


         Credit Suisse First Boston Venture Fund I, L.P.
         2400 Hanover Street
         Palo Alto, CA

         By:      QBB Management I, LLC, its General Partner

              By: /s/ Frank Quattrone
                 ------------------------------
                  Name: Frank Quattrone
                  Title:  Member


         Time Warner Telecom Inc.
         10475 Park Meadows Drive
         Suite 4400
         Littleton, CO  80124

              By: /s/ Paul B. Jones
                 ------------------------------
                  Name: Paul B. Jones
                  Title: Senior Vice President
                         General Counsel & Regulatory Policy


<PAGE>


         ICI Capital LLC
         3625 Queen Palm Drive
         Tampa, FL  33611

              By: /s/ Raymond L. Lawless
                 ------------------------------
                  Name: Raymond L. Lawless
                  Title: Vice President and Treasurer


         Williams Communications, Inc.
         One Williams Center
         Tulsa, OK  74172

              By: /s/ Dell B. [ILLEGIBLE]
                 ------------------------------
                  Name:
                  Title:


         Global Crossing Ventures, Inc.
         141 Caspian Court
         Sunnyvale, CA 94089

              By: /s/ Michael Cohen
                 ------------------------------
                  Name: Michael Cohen
                  Title:


         Z-Tel Technologies, Inc.
         601 S. Harbour Island Blvd.
         Suite 220
         Tampa, FL  33602

              By: /s/ Eduard J. Mayer
                 ------------------------------
                  Name: Eduard J. Mayer
                  Title: President

         Tailwind Capital Partners 2000, L.P.
         c/o Thomas Weisel Partners
         One Montgomery Street, Suite 3700
         San Francisco, CA  94104

         By:  Thomas Weisel Capital Partners LLC,
              its General Partner

              By: /s/ Marianne Winkler
                 ------------------------------
                  Name: Marianne Winkler
                  Title: CFO


<PAGE>


         Hambrecht & Quist California
         One Bush Street
         San Francisco, CA 94104

              By: /s/ Thomas Szymoniak
                 ------------------------------
                  Name: Thomas Szymoniak
                  Title: Attorney-in-Fact


         Hambrecht & Quist California
         One Bush Street
         San Francisco, CA 94104

              By: /s/ Thomas Szymoniak
                 ------------------------------
                  Name: Thomas Szymoniak
                  Title: Attorney-in-Fact


         H&Q Employee Venture Fund 2000, L.P.
         One Bush Street
         San Francisco, CA 94104


         By:  H&Q Venture Management LLC, its General Partner

              By: /s/ Thomas Szymoniak
                 ------------------------------
                  Name: Thomas Szymoniak
                  Title: Attorney-in-Fact


         Access Technology Partners, L.P.
         One Bush Street
         San Francisco, CA 94104


         By:  Access Technology Management LLC, its General Partner

              By: /s/ Thomas Szymoniak
                 ------------------------------
                  Name: Thomas Szymoniak
                  Title: Attorney-in-Fact


<PAGE>


         Access Technology Partners Brokers Fund, L.P.
         One Bush Street
         San Francisco, CA 94104


         By:  H&Q Venture Management, LLC, its General Partner

              By: /s/ Thomas Szymoniak
                 ------------------------------
                  Name: Thomas Szymoniak
                  Title: Attorney-in-Fact


         Viatel, Inc.
         685 Third Avenue,
         New York, NY 10017

              By: /s/ Sheldon M. Goldman
                 ------------------------------
                  Name: Sheldon M. Goldman
                  Title: EVP


         VYTL, LLC
         685 Third Avenue,
         New York, NY 10017

              By: /s/ Sheldon M. Goldman
                 ------------------------------
                  Name: Sheldon M. Goldman
                  Title:


         Eagle Teleprograms, Inc.
         60 East 56th Street
         New York, NY 10022

              By: /s/ Kent Srikanth Chargundla
                 ------------------------------
                  Name: Kent Srikanth Chargundla
                  Title: Chairman


         River Partners I
         c/o Tim Walsh
         1221 Avenue of the Americas
         New York, NY  10020

              By: /s/ Tim Walsh
                 ------------------------------
                  Name: Tim Walsh
                  Title: Managing Director


<PAGE>


         Carrier 1

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

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

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

              By:
                 ------------------------------
                  Name:
                  Title:


         Whitman Partners, L.P.

              By: /s/ Douglas Whitman
                 ------------------------------
                  Name:
                  Its: Manager


              By:
                 ------------------------------
                  Name:
                  Title:


<PAGE>


         U.S. Bancorp Piper Jaffray ECM Fund I, LLC
         222 South Ninth Street
         Minneapolis, MN  55402

              By: /s/ John Jacobs
                 ------------------------------
                  Name: John Jacobs
                  Title: Managing Member

         GD&C Partners 2000 Fund, LLC
         333 South Grand Avenue
         Los Angeles, CA  90071

              By:  /s/ [Illegible]
                 ------------------------------
                  Name:
                  Its:  Manager

<PAGE>


                                   SCHEDULE I
                                   ----------

<TABLE>
<CAPTION>
                NAME OF AND ADDRESS                           NO. OF SHARES OF                     AGGREGATE
                   OF PURCHASER                           SERIES D PREFERRED STOCK               PURCHASE PRICE
----------------------------------------------------    ------------------------------    -----------------------------
  <S>                                                   <C>                               <C>
  Credit Suisse First Boston Venture Fund I, L.P.
  2400 Hanover Street                                              297,257                       $4,875,014.80
  Palo Alto, CA

  Time Warner Telecom Inc.
  10475 Park Meadows Drive                                         182,927                       $3,000,002.80
  Suite 4400
  Littleton, CO  80124

  ICI Capital LLC
  3625 Queen Palm Drive                                            121,952                       $2,000,012.80
  Tampa, FL  33611

  BroadBand Office, Inc.
  2900 Telestar Court                                              121,952                       $2,000,012.80
  Falls Church, VA  22042

  Williams Communications, Inc.
  One Williams Center                                              91,464                        $1,500,009.60
  Tulsa, OK  74172

  Global Crossing Ventures, Inc.
  141 Caspian Court                                                60,976                        $1,000,006.40
  Sunnyvale, CA 94089

  Z-Tel Technologies, Inc.
  601 S. Harbour Island Blvd.                                      42,683                         $700,001.20
  Suite 220
  Tampa, FL  33602

  Tailwind Capital Partners 2000, L.P.
  c/o Thomas Weisel Partners                                       152,440                       $2,500,016.00
  One Montgomery Street, Suite 3700
  San Francisco, CA  94104

  Hambrecht & Quist California
  One Bush Street                                                  10,244                          $168,001.60
  San Francisco, CA 94104

  Hambrecht & Quist California
  One Bush Street                                                   6,098                          $100,007.20
  San Francisco, CA 94104



<PAGE>


  H&Q Employee Venture Fund 2000, L.P.
  One Bush Street                                                    6,098                         $100,007.20
  San Francisco, CA 94104

  Access Technology Partners, L.P.
  One Bush Street                                                   97,561                       $1,600,000.40
  San Francisco, CA 94104

  Access Technology Partners Brokers Fund, L.P.
  One Bush Street                                                    1,951                          $31,996.40
  San Francisco, CA 94104

  U.S. Bancorp Piper Jaffray ECM Fund I, LLC
  222 South Ninth Street                                            91,464                       $1,500,009.60
  Minneapolis, MN  55402

  Viatel, Inc.
  685 Third Avenue,                                                 60,976                       $1,000,006.40
  New York, NY 10017

  VYTL, LLC
  685 Third Avenue,                                                 18,293                         $300,005.20
  New York, NY 10017

  Eagle Teleprogramming, Inc.
  60 East 56th Street                                               15,244                         $250,001.60
  New York, NY 10022

  River Partners I
  c/o Tim Walsh                                                    60,976                        $1,000,006.40
  1221 Avenue of the Americas
  New York, NY  10020

  Whitman Partners, L.P.
  _______________                                                  60,976                        $1,000,006.40
  _______________

  Carrier 1
  _______________                                                  60,976                        $1,000,006.40
  _______________

  GD&C Partners 2000 Fund, LLC
  333 South Grand Avenue                                            7,622                         $125,000.80
  Los Angeles, CA 90071
 </TABLE>