EXHIBIT 10.25
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                                    GUARANTY
                                    --------

         GUARANTY, dated as of December 27, 2002, by VANTAGEPOINT VENTURE
PARTNERS III (Q), L.P., a Delaware limited partnership (the "Guarantor"), in
favor of FLEET NATIONAL BANK, a national banking association (the "Lender").

         WHEREAS, DSL.NET, INC., a Delaware corporation (the "Company"), has
entered into a Revolving Credit and Term Loan Agreement dated as of December 13,
2002 (as amended and in effect from time to time, the "Credit Agreement"), with
the Lender, pursuant to which the Lender, subject to the terms and conditions
contained therein, is to make loans or otherwise to extend to the Company;

         WHEREAS, the Guarantor owns certain of the capital stock of the
Company;

         WHEREAS, the Guarantor expects to receive substantial direct and
indirect benefits from the extensions of credit to the Company by the Lender
pursuant to the Credit Agreement (which benefits are hereby acknowledged);

         WHEREAS, it is a condition precedent to the Lender's making any loans
or otherwise extending credit to the Company under the Credit Agreement that the
Guarantor execute and deliver to the Lender a guaranty substantially in the form
hereof; and

         WHEREAS, the Guarantor wishes to guaranty the Company's obligations to
the Lender under or in respect of the Credit Agreement as provided herein;

         NOW, THEREFORE, the Guarantor hereby agrees with the Lender as follows:

         1. DEFINITIONS. Unless otherwise defined herein, all capitalized terms
used herein without definition shall have the respective meanings provided
therefor in the Credit Agreement.

         The term "Capital Call Obligation" means, as to the Guarantor, the
obligation of each Partner to pay his, her or its Unpaid Capital Commitment in
accordance with the terms and obligations of the Partnership Agreement of the
Guarantor.

         The term "Capital Commitment" means, as to the Guarantor, the total
amount agreed to be paid to the Guarantor by each Partner of the Guarantor, all
as set forth in the Partnership Agreement of the Guarantor.

         The term "Capital Contribution" means, as to the Guarantor, with
respect to any Partner of the Guarantor, that portion of such Partner's Capital
Commitment which has already been paid, funded or otherwise satisfied by such
Partner as of any date of determination.
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                                       -2-

         The term "Credit Agreement Guarantor" means a "Guarantor" as defined in
the Credit Agreement which has executed and delivered a Credit Agreement
Guaranty.

         The term "Credit Agreement Guaranty" means each "Guaranty" as defined
in the Credit Agreement, and which guaranty remains in full force and effect.

         The term "Defaulted Capital Call Obligations" means, as to the
Guarantor, any and all Capital Call Obligations of all Defaulting Partners, to
the extent that the Capital Commitments of such Defaulting Partners have not
otherwise been purchased by or allocated to other Partners of the Guarantor
which are not Defaulting Partners pursuant to the terms of the Partnership
Agreement of the Guarantor within thirty (30) days after any such Partner
becomes a Defaulting Partner.

         The term "Defaulting Partner" means, as to the Guarantor, any Partner
who or which (a) is considered a "Defaulting Limited Partner" under the terms of
the Partnership Agreement or (b) fails to pay any Capital Call Obligation on or
before the fifteenth (15th) Business Day following the date on which the General
Partner requires such payment pursuant to a written notice of a Capital Call to
such Partners, unless and until such failure to pay any such Capital Call
Obligation is subsequently cured or waived with the consent of, and to the
satisfaction of, the General Partner and the Lender.

         The term "Eligible Capital Call Commitments" means, as to the
Guarantor, the aggregate Capital Call Obligations of the Guarantor's Partners
(a) that are not subject to any lien, security interest or other encumbrance;
(b) that have not been paid (and are not the subject of any capital call which
has been made by the Guarantor's general partner but not yet funded by the
Partner and are not otherwise committed by such general partner) or otherwise
funded by the Partner or Partners; and (c) that do not include amounts with
respect to Defaulted Capital Call Obligations or (without duplication) amounts
with respect to any other Capital Call Obligations payable by a Defaulting
Partner.

         The term "General Partner" means VantagePoint Venture Associates III,
L.L.C., a Delaware limited liability company, in its capacity as general partner
of the Guarantor, or any Person substituted for or who succeeds VantagePoint
Venture Associates III, L.L.C. pursuant to the terms of the Partnership
Agreement and with the consent of the Lender.

         The term "Guarantor Credit Agreement" means that certain Revolving
Credit Agreement dated as of February 29, 2000 by and among the Guarantors,
Fleet National Bank and certain other lending institutions party thereto
(collectively, the "Credit Agreement Banks") and Fleet National Bank as agent
for such Credit Agreement Banks (the "Credit Agreement Agent"), as the same may
be amended, restated, supplemented and/or modified from time to time.
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                                       -3-

         The term "Indebtedness" shall mean, as to any individual, corporation,
partnership, trust, unincorporated association, business or other legal entity
and any government or any governmental agency or political subdivision thereof
(collectively, a "Person") and whether recourse is secured by or is otherwise
available against all or only a portion of the assets of such Person and whether
or not contingent, but without duplication: (i) every obligation of such Person
for money borrowed, (ii) every obligation of such Person evidenced by bonds,
debentures, notes or other similar instruments, including obligations incurred
in connection with the acquisition of property, assets or businesses, (iii)
every reimbursement obligation of such Person with respect to letters of credit,
bankers' acceptances or similar facilities issued for the account of such
Person, (iv) every obligation of such Person issued or assumed as the deferred
purchase price of property or services (including securities repurchase
agreements but excluding trade accounts payable or accrued liabilities arising
in the ordinary course of business which are not overdue or which are being
contested in good faith), (v) every obligation of such Person under any
capitalized lease, (vi) every obligation of such Person under any lease (a
"synthetic lease") treated as an operating lease under generally accepted
accounting principles and as a loan or financing for U.S. income tax purposes,
(vii) all sales by such Person of (A) accounts or general intangibles for money
due or to become due, (B) chattel paper, instruments or documents creating or
evidencing a right to payment of money or (C) other receivables (collectively
"receivables"), whether pursuant to a purchase facility or otherwise, other than
in connection with the disposition of the business operations of such Person
relating thereto or a disposition of defaulted receivables for collection and
not as a financing arrangement, and together with any obligation of such Person
to pay any discount, interest, fees, indemnities, penalties, recourse, expenses
or other amounts in connection therewith, (viii) every obligation of such Person
(an "equity related purchase obligation") to purchase, redeem, retire or
otherwise acquire for value any shares of capital stock of any class issued by
such Person, any warrants, options or other rights to acquire any such shares,
or any rights measured by the value of such shares, warrants, options or other
rights, (ix) every obligation of such Person under any forward contract, futures
contract, swap, option or other financing agreement or arrangement (including,
without limitation, caps, floors, collars and similar agreements), the value of
which is dependent upon interest rates, currency exchange rates, commodities or
other indices (a "derivative contract"), (x) every obligation in respect of
Indebtedness of any other entity (including any partnership in which such Person
is a general partner) to the extent that such Person is liable therefor as a
result of such Person's ownership interest in or other relationship with such
entity, except to the extent that the terms of such Indebtedness provide that
such Person is not liable therefor and such terms are enforceable under
applicable law, (xi) every obligation, contingent or otherwise, of such Person
guaranteeing, or having the economic effect of guarantying or otherwise acting
as surety for, any obligation of a type described in any of clauses (i) through
(x) (the "primary obligation") of another Person (the "primary obligor"), in any
manner, whether directly or indirectly, and including, without limitation, any
obligation of such Person (A) to purchase or pay (or advance or supply funds for
the purchase of) any security for the payment of such primary obligation, (B) to
purchase property, securities or services for the purpose of assuring the
payment of such primary obligation, or (C) to maintain working capital, equity
capital or other financial statement condition or liquidity of the primary
obligor so as to enable the primary obligor to pay such primary obligation.
<PAGE>
                                       -4-

         The term "Partner" means, as to the Guarantor, any Person who or which
holds a limited partnership interest in the Guarantor pursuant to the
Partnership Agreement of the Guarantor.

         The term "Partnership Agreement" shall mean the Limited Partnership
Agreement of VantagePoint Venture Partners III (Q), L.P. dated as of May 24,
1999 by and among the General Partner and the Partners.

         The term "Pro Rata Share" shall mean, as to each Credit Agreement
Guarantor, that portion of the principal amount of the Obligations which are
guaranteed by such Credit Agreement Guarantor pursuant to a Credit Agreement
Guaranty as compared to the principal amount of the Obligations which are
guaranteed by all Credit Agreement Guarantors pursuant to all Credit Agreement
Guarantees.

         The term "Related Guarantees" shall mean each Credit Agreement Guaranty
issued to the Lender from any Credit Agreement Guarantor other than the
Guarantor.

         The term "Total Guarantor Obligations" means, as to the Guarantor, the
sum of (a) the Obligations which are guaranteed by the Guarantor pursuant to
this Guaranty, plus (b) the sum of (i) outstanding Revolving Credit Loans (as
such term is defined in the Guarantor Credit Agreement) plus the Maximum Drawing
Amount (as such term is defined in the Guarantor Credit Agreement) of all issued
and outstanding Letters of Credit (as such term is defined in the Guarantor
Credit Agreement) plus all Unpaid Reimbursement Obligations (as such term is
defined in the Guarantor Credit Agreement) plus (ii) the aggregate amount of all
Indebtedness of the Guarantor consisting of the guarantees by the Guarantor of
the Indebtedness of any Portfolio Companies (as such term is defined under the
Partnership Agreement), provided, however, to the extent the Guarantor Credit
Agreement has been terminated, then (b)(i) hereof shall be the aggregate amount
of any obligations, whether contingent or otherwise, of the Guarantor for
borrowed money as of such date of determination.

         The term "Unpaid Capital Commitment" means, as to the Guarantor, with
respect to any Partner of the Guarantor, such Partner's Capital Commitment less
such Partner's Capital Contribution.

         2. GUARANTY OF PAYMENT AND PERFORMANCE. The Guarantor hereby guarantees
to the Lender the full and punctual payment when due (whether at stated
maturity, by required pre-payment, by acceleration or otherwise), as well as the
performance, of all of the Obligations including all such which would become due
but for the operation of the automatic stay pursuant to ss.362(a) of the Federal
Bankruptcy Code and the operation of ss.ss.502(b) and 506(b) of the Federal
Bankruptcy Code. In addition, the Guarantor agrees that payments by the
Guarantor hereunder shall be made without recoupment, setoff or counterclaim and
free and clear of and without deduction for any taxes, levies, imposts, duties,
charges, fees, deductions, withholdings, compulsory loans, restrictions or
conditions of any nature now or hereafter imposed or levied by any jurisdiction
or any political subdivision thereof or taxing or other authority therein unless
the Guarantor is compelled by law to make such deduction or withholding. If any
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                                       -5-

such obligation is imposed upon the Guarantor with respect to any amount payable
by it hereunder or under any of the other Loan Documents, the Guarantor will pay
to the Lender, on the date on which such amount is due and payable under any
Loan Document, such additional amount in United States dollars as shall be
necessary to enable the Lender to receive the same net amount which the Lender
would have received on such due date had no such obligation been imposed upon
the Guarantor. This Guaranty is an absolute, unconditional and continuing
guaranty of the full and punctual payment and performance of all of the
Obligations and not of their collectibility only and is in no way conditioned
upon any requirement that the Lender first attempt to collect any of the
Obligations from the Company or resort to any collateral security or other means
of obtaining payment. Should the Company default in the payment or performance
of any of the Obligations, the obligations of the Guarantor hereunder with
respect to such Obligations in default shall, upon demand by the Lender, become
immediately due and payable to the Lender, without demand or notice of any
nature, all of which are expressly waived by the Guarantor. Payments by the
Guarantor hereunder may be required by the Lender on any number of occasions.

         3. GUARANTOR'S AGREEMENT TO PAY ENFORCEMENT COSTS, ETC. The Guarantor
further agrees, as the principal obligor and not as a guarantor only, to pay to
the Lender, on demand, all reasonable costs and expenses (including court costs
and legal expenses) incurred or expended by the Lender in connection with the
Obligations, this Guaranty and the enforcement thereof, together with interest
on amounts recoverable under this ss.3 from the time when such amounts become
due until payment, whether before or after judgment, at the rate of interest for
overdue principal set forth in the Note, provided that if such interest exceeds
the maximum amount permitted to be paid under applicable law, then such interest
shall be reduced to such maximum permitted amount.

         4. LIMITED GUARANTY. Notwithstanding any other term or provision of
this Guaranty to the contrary, the Guarantor's liability hereunder shall be
limited to an amount equal to (a) $5,000,000 in principal amount, plus, without
limitation as to the amounts thereof, (b) the Guarantor's Pro Rata Share of all
interest, banking charges, commissions, costs and reasonable expenses chargeable
to the Company in respect of the Obligations (other than costs and expenses,
including attorneys fees, incurred in connection with the enforcement against
the Company of the Credit Agreement or other Loan Documents, unless the Lender
is required to incur just costs and/or expenses prior to being able to demand
payment hereunder), plus (c) the Guarantor's Pro Rata Share of all interest and
other costs and reasonable expenses payable by the Guarantor pursuant to ss.3
hereof (other than costs and expenses, including attorneys fees, incurred in
connection with the enforcement against the Company of the Credit Agreement or
other Loan Documents, unless the Lender is required to incur just costs and/or
expenses prior to being able to demand payment hereunder), provided, the
Guarantor shall pay all of the costs and expenses incurred or expended by the
Lender in connection with this Guaranty and the enforcement thereof. Each
payment made by the Guarantor hereunder which is applied against the Obligations
referred to in clause (a) above shall reduce the Guarantor's liability by such
amount. The Lender's dealings with the Company need not be limited to any
particular sum notwithstanding any limitation herein upon the liability of the
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                                       -6-

Guarantor. The Lender hereby agrees that to the extent it shall require any
payments be made hereunder, the Lender will, to the extent permissable,
simultaneously make a claim for payment on all Credit Agreement Guarantees such
that any payment being required to be made hereunder will not exceed the
Guarantor's Pro Rata Share of the aggregate amount being claimed by the Lender
under all Credit Agreement Guarantees (and, to the extent the Lender is not
permitted or otherwise able to make a claim under any Credit Agreement Guaranty,
the Lender shall be deemed to have made such a claim under such Credit Agreement
Guaranty for purposes of this sentence).

         5. WAIVERS BY GUARANTOR; LENDER'S FREEDOM TO ACT. The Guarantor agrees
that the Obligations will be paid and performed strictly in accordance with
their respective terms, regardless of any law, regulation or order now or
hereafter in effect in any jurisdiction affecting any of such terms or the
rights of the Lender with respect thereto. The Guarantor waives promptness,
diligences, presentment, demand, protest, notice of acceptance, notice of any
Obligations incurred and all other notices of any kind, all defenses which may
be available by virtue of any valuation, stay, moratorium law or other similar
law now or hereafter in effect, any right to require the marshalling of assets
of the Company or any other entity or other person primarily or secondarily
liable with respect to any of the Obligations, and all suretyship defenses
generally. Without limiting the generality of the foregoing, the Guarantor
agrees to the provisions of any instrument evidencing, securing or otherwise
executed in connection with any Obligation and agrees that the obligations of
the Guarantor hereunder shall not be released or discharged, in whole or in
part, or otherwise affected by (a) the failure of the Lender to assert any claim
or demand or to enforce any right or remedy against the Company or any other
entity or other person primarily or secondarily liable with respect to any of
the Obligations; (b) any extensions, compromise, refinancing, consolidation or
renewals of any Obligation; (c) any change in the time, place or manner of
payment of any of the Obligations or any rescissions, waivers, compromise,
refinancing, consolidation, amendments or modifications of any of the terms or
provisions of the Credit Agreement, the other Loan Documents or any other
agreement evidencing, securing or otherwise executed in connection with any of
the Obligations; (d) the addition, substitution or release of any entity or
other person primarily or secondarily liable for any Obligation, (e) the
adequacy of any rights which the Lender may have against any collateral security
or other means of obtaining repayment of any of the Obligations; (f) the
impairment of any collateral securing any of the Obligations, including without
limitation the failure to perfect or preserve any rights which the Lender might
have in such collateral security or the substitution, exchange, surrender,
release, loss or destruction of any such collateral security; or (g) any other
act or omission which might in any manner or to any extent vary the risk of the
Guarantor or otherwise operate as a release or discharge of the Guarantor, all
of which may be done without notice to the Guarantor. To the fullest extent
permitted by law, the Guarantor hereby expressly waives any and all rights or
defenses arising by reason of (i) any "one action" or "anti-deficiency" law
which would otherwise prevent the Lender from bringing any action, including any
claim for a deficiency, or exercising any other right or remedy (including any
right of set-off), against the Guarantor before or after the Lender's
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                                       -7-

commencement or completion of any foreclosure action, whether judicially, by
exercise of power of sale or otherwise, or (ii) any other law which in any other
way would otherwise require any election of remedies by the Lender.

         6. UNENFORCEABILITY OF OBLIGATIONS AGAINST COMPANY. If for any reason
the Company has no legal existence or is under no legal obligation to discharge
any of the Obligations, or if any of the Obligations have become irrecoverable
from the Company by reason of the Company's insolvency, bankruptcy or
reorganization or by other operation of law or for any other reason, this
Guaranty shall nevertheless be binding on the Guarantor to the same extent as if
the Guarantor at all times had been the principal obligor on all such
Obligations. In the event that acceleration of the time for payment of any of
the Obligations is stayed upon the insolvency, bankruptcy or reorganization of
the Company, or for any other reason, all such amounts otherwise subject to
acceleration under the terms of the Credit Agreement, the other Loan Documents
or any other agreement evidencing, securing or otherwise executed in connection
with any Obligation shall be immediately due and payable by the Guarantor.

         7.  SUBROGATION; SUBORDINATION.

                  7.1. WAIVER OF RIGHTS AGAINST COMPANY. Until the final payment
         and performance in full of all of the Obligations, the Guarantor shall
         not exercise any rights against the Company arising as a result of
         payment by the Guarantor hereunder, by way of subrogation,
         reimbursement, restitution, contribution or otherwise, and will not
         prove any claim in competition with the Lender in respect of any
         payment hereunder in any bankruptcy, insolvency or reorganization case
         or proceedings of any nature; the Guarantor will not claim any setoff,
         recoupment or counterclaim against the Company in respect of any
         liability of the Guarantor to the Company; and the Guarantor waives any
         benefit of and any right to participate in any collateral security
         which may be held by the Lender.

                  7.2. SUBORDINATION. The payment of any amounts due with
         respect to any indebtedness of the Company now or hereafter owed to the
         Guarantor is hereby subordinated to the prior payment in full of all of
         the Obligations, to the extent and in the manner set forth in the next
         sentence. The Guarantor agrees that, after the occurrence and during
         the continuance of any default in the payment or performance of any of
         the Obligations, the Guarantor will not demand, sue for or otherwise
         attempt to collect any such indebtedness of the Company to the
         Guarantor until all of the Obligations shall have been paid in full.
         If, notwithstanding the foregoing sentence, the Guarantor shall
         collect, enforce or receive any amounts in respect of such
         indebtedness, such amounts shall be collected, enforced and received by
         the Guarantor as trustee for the Lender and be paid over to the Lender
         on account of the Obligations without affecting in any manner the
         liability of the Guarantor under the other provisions of this Guaranty.
<PAGE>
                                       -8-

                  7.3. PROVISIONS SUPPLEMENTAL. The provisions of this ss.7
         shall be supplemental to and not in derogation of any rights and
         remedies of the Lender under any separate subordination agreement which
         the Lender may at any time and from time to time enter into with the
         Guarantor.

         8. SECURITY; SETOFF. The Guarantor grants to the Lender, as security
for the full and punctual payment and performance of all of the Guarantor's
obligations hereunder, a continuing lien on and security interest in all
securities or other property belonging to the Guarantor now or hereafter held by
the Lender and in all deposits (general or special, time or demand, provisional
or final) and other sums credited by or due from the Lender to the Guarantor or
subject to withdrawal by the Guarantor. Regardless of the adequacy of any
collateral security or other means of obtaining payment of any of the
Obligations, the Lender is hereby authorized at any time and from time to time,
without notice to the Guarantor (any such notice being expressly waived by the
Guarantor) and to the fullest extent permitted by law, to set off and apply such
deposits and other sums against the obligations of the Guarantor under this
Guaranty, whether or not the Lender shall have made any demand under this
Guaranty and although such obligations may be contingent or unmatured.

         9.  REPRESENTATIONS; COVENANTS AND FURTHER ASSURANCES.

                  9.1. REPRESENTATIONS. Each of the Guarantor and the General
         Partner, in its capacity as sole general partner of the Guarantor
         hereby represents and warrants to the Lender that (a) each of the
         Guarantor and General Partner is duly organized, validly existing, and
         in good standing under the laws of its jurisdiction of formation, and
         the execution, delivery and performance by the Guarantor and the
         General Partner of this Guaranty and the other Loan Documents to which
         it is a party (i) are within its partnership or limited liability
         company (as the case may be) authority, (ii) have been duly authorized
         by all appropriate action, (iii) do not conflict with or contravene its
         Partnership Agreement, operating agreement, or any law, rule, order or
         regulation; (b) upon the execution and delivery thereof, the Guaranty
         and each other Loan Document shall constitute the legal, valid and
         binding obligation of the Guarantor party thereto, enforceable in
         accordance with its terms; (c) the financial statements provided to the
         Lender as at September 30, 2002 are complete and correct and fairly
         present the position of the Guarantor as at such date and for such
         period in accordance with generally accepted accounting principles
         consistently applied; and (d) the execution, delivery, performance of
         its obligations, and exercise of its rights under the Guaranty and the
         other Loan Documents by the Guarantor (i) do not require any consents
         or approvals; and (ii) are not and will not be in conflict with or
         prohibited or prevented by (A) any law, rule, order or regulation, or
         (B) its Partnership Agreement or any partnership action.

                  9.2. COVENANTS. The Guarantor agrees that at all times the
         ratio of (a) Eligible Capital Call Commitments of the Guarantor to (b)
         Total Guarantor Obligations of the Guarantor shall not be less than
         1.33:1.00. Not later than forty-five (45) days after the end of each
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                                       -9-

         fiscal quarter, the Guarantor shall provide to the Lender evidence
         demonstrating compliance with this covenant contained in ss.9.2 To the
         extent the ratio of (a) Eligible Capital Call Commitments of a
         Guarantor to (b) Total Guarantor Obligations for the Guarantor is less
         than 1.33:1.00, upon demand by the Lender, the Guarantor shall deposit
         with the Lender cash collateral in an amount sufficient so that when
         added to the Eligible Capital Call Commitment portion of such ratio,
         the Guarantor complies with the covenant set forth in this ss.9.2. In
         addition, the Guarantor agrees that so long as any Obligation is
         outstanding, the Guarantor will not (1) create, incur, assume,
         guarantee or be or remain liable, contingently or otherwise, with
         respect to any Indebtedness other than Indebtedness permitted by ss.7.1
         of the Guarantor Credit Agreement; (2) create or incur or suffer to be
         created or incurred or permit to exist any lien, encumbrance, mortgage,
         pledge, charge, restriction or other security interest of any kind upon
         any Capital Call Obligation or the Guarantor's rights to receive such
         payments, or (3) or enter into any agreement prohibiting the creation
         or assumption of any lien upon its properties, revenues or assets,
         whether now owned or hereafter acquired, unless otherwise permitted by
         the Guarantor Credit Agreement.

                  9.3. FURTHER ASSURANCES. The Guarantor agrees that it will
         from time to time, at the request of the Lender, provide to the Lender
         the Guarantor's most recent audited and unaudited balance sheets and
         related statements of income and changes in financial condition and
         such other information relating to the business and affairs of the
         Guarantor as the Lender may reasonably request. The Guarantor also
         agrees to do all such things and execute all such documents as the
         Lender may consider reasonably necessary or desirable to give full
         effect to this Guaranty and to perfect and preserve the rights and
         powers of the Lender hereunder. The Guarantor acknowledges and confirms
         that the Guarantor itself has established its own adequate means of
         obtaining from the Company on a continuing basis all information
         desired by the Guarantor concerning the financial condition of the
         Company and that the Guarantor will look to the Company and not to the
         Lender in order for the Guarantor to keep adequately informed of
         changes in the Company's financial condition.

         10. TERMINATION; REINSTATEMENT. This Guaranty shall remain in full
force and effect until the Lender is given written notice of the Guarantor's
intention to discontinue this Guaranty, notwithstanding any intermediate or
temporary payment or settlement of the whole or any part of the Obligations. No
such notice shall be effective unless received and acknowledged by an officer of
the Lender at the address of the Lender for notices set forth in the Credit
Agreement. No such notice shall affect any rights of the Lender hereunder,
including without limitation the rights set forth in ss.ss.5 and 7, with respect
to any Obligations incurred or accrued prior to the receipt of such notice or
any Obligations incurred or accrued pursuant to any contract or commitment in
existence prior to such receipt, and all checks, drafts, notes, instruments
(negotiable or otherwise) and writings made by or for the account of the Company
and drawn on the Lender or any of its agents purporting to be dated on or before
the date of receipt of such notice, although presented to and paid or accepted
by the Lender after that date, shall form part of the Obligations. This Guaranty
<PAGE>
                                      -10-

shall continue to be effective or be reinstated, notwithstanding any such
notice, if at any time any payment made or value received with respect to any
Obligation is rescinded or must otherwise be returned by the Lender upon the
insolvency, bankruptcy or reorganization of the Company, or otherwise, all as
though such payment had not been made or value received. In addition, promptly
after the Obligations have been indefeasibly repaid in full in cash and all
Commitments have been terminated, the Lender will return to the Guarantor the
Guaranty marked "terminated" and/or "cancelled".

         11. SUCCESSORS AND ASSIGNS. This Guaranty shall be binding upon the
Guarantor, its successors and assigns, and shall inure to the benefit of and be
enforceable by the Lender and its successors, transferees and assigns. Without
limiting the generality of the foregoing sentence, the Lender may assign or
otherwise transfer the Credit Agreement, the other Loan Documents or any other
agreement or note held by it evidencing, securing or otherwise executed in
connection with the Obligations, or sell participations in any interest therein,
to any other entity or other person, and such other entity or other person shall
thereupon become vested, to the extent set forth in the agreement evidencing
such assignment, transfer or participation, with all the rights in respect
thereof granted to the Lender herein. The Guarantor may not assign any of its
obligations hereunder.

         12. AMENDMENTS AND WAIVERS. No amendment or waiver of any provision of
this Guaranty nor consent to any departure by the Guarantor therefrom shall be
effective unless the same shall be in writing and signed by the Guarantor and
the Lender. No failure on the part of the Lender to exercise, and no delay in
exercising, any right hereunder shall operate as a waiver thereof; nor shall any
single or partial exercise of any right hereunder preclude any other or further
exercise thereof or the exercise of any other right.

         13. NOTICES. All notices and other communications called for hereunder
shall be made in writing and, unless otherwise specifically provided herein,
shall be deemed to have been duly made or given when delivered by hand or mailed
first class, postage prepaid, or, in the case of telegraphic or telexed notice,
when transmitted, answer back received, addressed as follows: if to the
Guarantor, at the address set forth beneath its signature hereto, and if to the
Lender, at the address for notices to the Lender set forth in the Credit
Agreement, or at such address as either party may designate in writing to the
other.

         14. GOVERNING LAW; CONSENT TO JURISDICTION. THIS GUARANTY IS INTENDED
TO TAKE EFFECT AS A SEALED INSTRUMENT AND SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS. The Guarantor
agrees that any suit for the enforcement of this Guaranty may be brought in the
courts of the Commonwealth of Massachusetts or any federal court sitting therein
and consents to the nonexclusive jurisdiction of such court and to service of
process in any such suit being made upon the Guarantor by mail at the address
specified by reference in ss.13. The Guarantor hereby waives any objection that
<PAGE>
                                      -11-


it may now or hereafter have to the venue of any such suit or any such court or
that such suit was brought in an inconvenient court.

         15. WAIVER OF JURY TRIAL. THE GUARANTOR HEREBY WAIVES ITS RIGHT TO A
JURY TRIAL WITH RESPECT TO ANY ACTION OR CLAIM ARISING OUT OF ANY DISPUTE IN
CONNECTION WITH THIS GUARANTY, ANY RIGHTS OR OBLIGATIONS HEREUNDER OR THE
PERFORMANCE OF ANY OF SUCH RIGHTS OR OBLIGATIONS. Except as prohibited by law,
the Guarantor hereby waives any right which it may have to claim or recover in
any litigation referred to in the preceding sentence any special, exemplary,
punitive or consequential damages or any damages other than, or in addition to,
actual damages. The Guarantor (a) certifies that neither the Lender nor any
representative, agent or attorney of the Lender has represented, expressly or
otherwise, that the Lender would not, in the event of litigation, seek to
enforce the foregoing waivers and (b) acknowledges that, in entering into the
Credit Agreement and the other Loan Documents to which the Lender is a party,
the Lender is relying upon, among other things, the waivers and certifications
contained in this ss.15.

         16. MISCELLANEOUS. This Guaranty constitutes the entire agreement of
the Guarantor and the Lender with respect to the matters set forth herein. The
rights and remedies herein provided are cumulative and not exclusive of any
remedies provided by law or any other agreement, and this Guaranty shall be in
addition to any other guaranty of or collateral security for any of the
Obligations. The invalidity or unenforceability of any one or more sections of
this Guaranty shall not affect the validity or enforceability of its remaining
provisions. Captions are for the ease of reference only and shall not affect the
meaning of the relevant provisions. The meanings of all defined terms used in
this Guaranty shall be equally applicable to the singular and plural forms of
the terms defined.
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                                      -12-


         IN WITNESS WHEREOF, the Guarantor has caused this Guaranty to be
executed and delivered as of the date first above written.


                                    VANTAGEPOINT VENTURE PARTNERS III (Q), L.P.
                                    By:  VantagePoint Venture Associates III,
                                    LLC, its General Partner


                                    By: /s/ James D. Marver
                                        -------------------------------------
                                        Name: James D. Marver
                                        Title:
                                        Address: