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                                                                   EXHIBIT 10.46

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                          iBASIS SECURITIES CORPORATION

                                    GUARANTEE

                          Dated as of February 21, 2003

               U.S. Bank National Association, as Collateral Agent

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                                TABLE OF CONTENTS

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<S>                                                                                        <C>
1.   Reference to Exchange Agreement; Definitions; Certain Rules of Construction...........1
     1.1.    "Agreement"...................................................................1
     1.2.    "Obligors"....................................................................1
2.   Guarantee.............................................................................2
     2.1.    Guarantee of Obligations......................................................2
     2.2.    Continuing Obligation.........................................................2
     2.3.    Waivers with Respect to Obligations...........................................3
     2.4.    Investors' Power to Waive, etc................................................4
     2.5.    Information Regarding the Borrower, etc.......................................5
     2.6.    Certain Guarantor Representations.............................................5
     2.7.    Subrogation...................................................................6
     2.8.    Subordination.................................................................6
     2.9.    Future Subsidiaries; Further Assurances.......................................6
3.   Representations and Warranties........................................................7
     3.1.    Organization and Business.....................................................7
     3.2.    Authorization and Enforceability..............................................7
     3.3.    No Legal Obstacle to Agreements...............................................7
     3.4.    Litigation....................................................................7
4.   Successors and Assigns................................................................8
5.   Notices...............................................................................8
6.   Reimbursement of Expenses.............................................................8
7.   Venue; Service of Process.............................................................8
8.   WAIVER OF JURY TRIAL..................................................................9
9.   General...............................................................................9
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                          iBASIS SECURITIES CORPORATION

                                    GUARANTEE

     This Agreement, dated as of February 21, 2003, is among iBasis Securities
Corporation, a Massachusetts corporation (the "GUARANTOR"), and U.S. Bank
National Association, as Collateral Agent (the "COLLATERAL AGENT") for itself
and the Holders under the Exchange Agreement (as defined below). The parties
agree as follows:

1.   REFERENCE TO EXCHANGE AGREEMENT; DEFINITIONS; CERTAIN RULES OF
CONSTRUCTION. Reference is made to the Securities Exchange Agreement dated as of
the date hereof, as from time to time in effect (the "EXCHANGE AGREEMENT"),
among iBasis, Inc., a Delaware corporation (the "COMPANY"), iBasis Global, Inc.,
a Delaware corporation ("iBASIS GLOBAL", and collectively with the Company, the
"BORROWER"), the Guarantor, the Exchanging Holders named therein and the
Collateral Agent. Capitalized terms defined in the Exchange Agreement and not
otherwise defined herein are used herein with the meanings so defined. Certain
other capitalized terms are used in this Agreement as specifically defined below
in this Section 1. Except as the context otherwise explicitly requires, (a) the
capitalized term "Section" refers to sections of this Agreement, (b) the
capitalized term "Exhibit" refers to exhibits to this Agreement, (c) references
to a particular Section shall include all subsections thereof, (d) the word
"including" shall be construed as "including without limitation", (e) references
to a particular statute or regulation include all rules and regulations
thereunder and any successor statute, regulation or rules, in each case as from
time to time in effect and (f) references to a particular Person include such
Person's successors and assigns to the extent not prohibited by this Agreement
and the other Credit Documents. References to "the date hereof" mean the date
first set forth above.

     1.1. "AGREEMENT" means this Guarantee as from time to time in effect.

     1.2. "EXCHANGING HOLDERS" means the Exchanging Holders from time to time
signatories to the Exchange Agreement and any other holders of Convertible Notes
who (i) become parties to the Exchange Agreement pursuant to the execution and
delivery of a Joinder Agreement in accordance with the terms of the Exchange
Agreement or (ii) exchange their Convertible Notes for Notes pursuant to a
Permitted Exchange.

     1.3. "OBLIGATIONS" means any and all present and future liabilities,
obligations and Indebtedness of the Borrower and any of its Subsidiaries or any
other Obligor owing to the Collateral Agent or any Holder (or any Affiliate of a
Holder or Collateral Agent) under or in connection with the Exchange Agreement,
any other Credit Document or any other agreement executed in connection with a
Permitted Exchange, including, without limitation, obligations in respect of
principal, interest, prepayment premium and all other reimbursement obligations
under the Notes, all fees, charges, indemnities and expenses from time to time
owing hereunder, under any other Credit Document and under any other agreement
executed in connection with a

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Permitted Exchange (all whether accruing before or after a Bankruptcy Default
and regardless of whether allowed as a claim in bankruptcy or similar
proceedings).

     1.4. "OBLIGORS" means the Borrower, the Guarantor and the Subsidiaries of
the Borrower party hereto as guarantors from time to time.

2.   GUARANTEE.

     2.1. GUARANTEE OF OBLIGATIONS. The Guarantor unconditionally guarantees
that the Obligations will be performed and paid in full in cash when due and
payable, whether at the stated or accelerated maturity thereof or otherwise,
this guarantee being a guarantee of payment and not of collectability and being
absolute and in no way conditional or contingent. In the event any part of the
Obligations shall not have been so paid in full when due and payable, the
Guarantor will, immediately upon notice by the Collateral Agent or, without
notice, immediately upon the occurrence of a Bankruptcy Default, pay or cause to
be paid to the Collateral Agent for the account of each Holder in accordance
with the Holder's respective Percentage Interests therein the amount of such
Obligations which are then due and payable and unpaid. The obligations of the
Guarantor hereunder shall not be affected by the invalidity, unenforceability or
irrecoverability of any of the Obligations as against the Borrower, any other
Obligor, any other guarantor thereof or any other Person. For purposes hereof,
the Obligations shall be due and payable when and as the same shall be due and
payable under the terms of the Exchange Agreement or any other Credit Document
notwithstanding the fact that the collection or enforcement thereof may be
stayed or enjoined under the Bankruptcy Code or other applicable law.

     2.2. CONTINUING OBLIGATION. The Guarantor acknowledges that the Exchanging
Holders have entered into the Exchange Agreement (and, to the extent that the
Exchanging Holders, any Holder or holder of any interest in the Obligations or
the Collateral Agent may enter into any future Credit Document, will have
entered into such agreement) in reliance on this Section 2 being a continuing
irrevocable agreement, and the Guarantor agrees that its guarantee may not be
revoked in whole or in part. The obligations of the Guarantor hereunder shall
terminate when all of the Obligations have been indefeasibly paid in full in
cash and discharged; PROVIDED, HOWEVER, that if a claim is made upon the Holders
at any time for repayment or recovery of any amounts or any property received by
the Holders from any source on account of any of the Obligations and the Holders
repay or return any amounts or property so received (including interest thereon
to the extent required to be paid by the Holders), then the Guarantor shall
remain liable under this Agreement for the amounts so repaid or property so
returned or the amounts for which the Holders become liable (such amounts being
deemed part of the Obligations) to the same extent as if such amounts or
property had never been received by the Holders, notwithstanding any termination
hereof or the cancellation of any instrument or agreement evidencing any of the
Obligations. Not later than five days after receipt of notice from the
Collateral Agent, the Guarantor shall pay to the Collateral Agent an amount
equal to the amount of such repayment or return for which the Holders have so
become liable. Payments

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hereunder by the Guarantor may be required by the Collateral Agent on any number
of occasions.

     2.3. WAIVERS WITH RESPECT TO OBLIGATIONS. Except to the extent expressly
required by the Exchange Agreement or any other Credit Document, the Guarantor
waives, to the fullest extent permitted by the provisions of applicable law, all
of the following (including all defenses, counterclaims and other rights of any
nature based upon any of the following):

          (a)  presentment, demand for payment and protest of nonpayment of any
     of the Obligations, and notice of protest, dishonor or nonperformance;

          (b)  notice of acceptance of this guarantee and notice that credit has
     been extended in reliance on the Guarantor's guarantee of the Obligations;

          (c)  notice of any Event of Default or of any inability to enforce
     performance of the obligations of the Borrower or any other Person with
     respect to any Credit Document or notice of any acceleration of maturity of
     any Obligations;

          (d)  demand for performance or observance of, and any enforcement of
     any provision of the Exchange Agreement, the Obligations or any other
     Credit Document or any pursuit or exhaustion of rights or remedies with
     respect to any Credit Security or against the Borrower or any other Person
     in respect of the Obligations or any requirement of diligence or promptness
     on the part of the Collateral Agent or the Holders in connection with any
     of the foregoing;

          (e)  any act or omission on the part of the Collateral Agent or the
     Holders which may impair or prejudice the rights of the Guarantor,
     including rights to obtain subrogation, exoneration, contribution,
     indemnification or any other reimbursement from the Borrower or any other
     Person, or otherwise operate as a deemed release or discharge;

          (f)  failure or delay to perfect or continue the perfection of any
     security interest in any Credit Security or any other action which harms or
     impairs the value of, or any failure to preserve or protect the value of,
     any Credit Security;

          (g)  any statute of limitations or any statute or rule of law which
     provides that the obligation of a surety must be neither larger in amount
     nor in other respects more burdensome than the obligation of the principal;

          (h)  any "single action" or "anti-deficiency" law which would
     otherwise prevent the Holders from bringing any action, including any claim
     for a deficiency, against the Guarantor before or after the Collateral
     Agent's or the Holders' commencement or completion of any foreclosure
     action, whether judicially, by exercise of power of sale or otherwise, or
     any other law which would otherwise require any election of remedies by the
     Collateral Agent or the Holders;

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          (i)  all demands and notices of every kind with respect to the
     foregoing; and

          (j)  to the extent not referred to above, all defenses (other than
     payment) which the Borrower may now or hereafter have to the payment of the
     Obligations, together with all suretyship defenses, which could otherwise
     be asserted by the Guarantor.

Each Guarantor represents that it has obtained the advice of counsel as to the
extent to which suretyship and other defenses may be available to it with
respect to its obligations hereunder in the absence of the waivers contained in
this Section 2.3.

     No delay or omission on the part of the Collateral Agent or the Holders in
exercising any right under any other Credit Document or under any other
guarantee of the Obligations or with respect to the Credit Security shall
operate as a waiver or relinquishment of such right. Absent gross negligence or
willful misconduct on the Collateral Agent's or Holders' part, no action which
the Collateral Agent or the Holders or the Borrower or any other Obligor may
take or refrain from taking with respect to the Obligations shall affect the
provisions of this Agreement or the obligations of the Guarantor hereunder. None
of the Holders' or the Collateral Agent's rights shall at any time in any way be
prejudiced or impaired by any act or failure to act on the part of the Borrower
or any other Obligor, or by any noncompliance by the Borrower or any other
Obligor with any Credit Document, regardless of any knowledge thereof which the
Collateral Agent or the Holders may have or otherwise be charged with.

     2.4. HOLDERS' POWER TO WAIVE, ETC. The Guarantor grants to the Collateral
Agent and the Holders full power in their discretion, without notice to or
consent of the Guarantor, such notice and consent being expressly waived to the
fullest extent permitted by applicable law, and without in any way affecting the
liability of the Guarantor under its guarantee hereunder:

          (a)  To waive compliance with, and any Default under, and to consent
     to any amendment to or modification or termination of any provision of, or
     to give any waiver in respect of, the Exchange Agreement, any other Credit
     Document, the Credit Security, the Obligations or any guarantee thereof
     (each as from time to time in effect);

          (b)  To grant any extensions of the Obligations (for any duration),
     and any other indulgence with respect thereto, and to effect any total or
     partial release (by operation of law or otherwise), discharge, compromise
     or settlement with respect to the obligations of the Obligors or any other
     Person in respect of the Obligations, whether or not rights against the
     Guarantor under this Agreement are reserved in connection therewith;

          (c)  To take security in any form for the Obligations, and to consent
     to the addition to or the substitution, exchange, release or other
     disposition of, or to deal in any other manner with, any part of any
     property contained in the Credit Security whether or not the property, if
     any, received upon the exercise of such power shall be of a character or
     value the same as or different from the character or value of any property
     disposed of,

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     and to obtain or release any present or future guarantees of the
     Obligations and to proceed against any of the Credit Security or such
     guarantees in any order;

          (d)  To collect or liquidate or realize upon any of the Obligations or
     the Credit Security in a commercially reasonable manner or to refrain from
     collecting or liquidating or realizing upon any of the Obligations or the
     Credit Security; and

          (e)  To extend credit under the Exchange Agreement, any other Credit
     Document or otherwise in such amount as the Holders may determine,
     including increasing the amount of credit and the interest rate and fees
     with respect thereto, even though the condition of the Obligors (financial
     or otherwise, on an individual or Consolidated basis) may have deteriorated
     since the date hereof.

     2.5. INFORMATION REGARDING THE BORROWER, ETC. The Guarantor has made such
investigation as it deems desirable of the risks undertaken by them in entering
into this Agreement and are fully satisfied that it understands all such risks.
The Guarantor waives any obligation which may now or hereafter exist on the part
of the Collateral Agent or the Holders to inform it of the risks being
undertaken by entering into this Agreement or of any changes in such risks and,
from and after the date hereof, the Guarantor undertakes to keep themselves
informed of such risks and any changes therein. The Guarantor expressly waives
any duty which may now or hereafter exist on the part of the Collateral Agent or
the Holders to disclose to such Guarantor any matter related to the business,
operations, character, collateral, credit, condition (financial or otherwise),
income or prospects of the Borrower and its Affiliates or their properties or
management, whether now or hereafter known by the Collateral Agent or the
Holders. The Guarantor represents, warrants and agrees that it assumes sole
responsibility for obtaining from the Borrower all information concerning the
Exchange Agreement and all other Credit Documents and all other information as
to the Borrower and its Affiliates or their properties or management as the
Guarantor deems necessary or desirable.

     2.6. CERTAIN GUARANTOR REPRESENTATIONS.  Each Guarantor represents that:

          (a)  it is in its best interest and in pursuit of the purposes for
     which it was organized as an integral part of the business conducted and
     proposed to be conducted by the Borrower and its Subsidiaries, and
     reasonably necessary and convenient in connection with the conduct of the
     business conducted and proposed to be conducted by them, to induce the
     Exchanging Holders to enter into the Exchange Agreement and to extend
     credit to the Guarantor by making the Guarantee contemplated by this
     Section 2;

          (b)  the credit available under the Exchange Agreement will directly
     or indirectly inure to its benefit;

          (c)  by virtue of the foregoing it is receiving at least reasonably
     equivalent value from the Exchanging Holders for its Guarantee;

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          (d)  it will not be rendered insolvent as a result of entering into
     his Agreement;

          (e)  after giving effect to the transactions contemplated by this
     Agreement, it will have assets having a fair saleable value in excess of
     the amount required to pay its probable liability on its existing debts as
     such debts become absolute and matured;

          (f)  it has, and will have, access to adequate capital for the conduct
     of its business;

          (g)  it has the ability to pay its debts from time to time incurred in
     connection therewith as such debts mature; and

          (h)  it has been advised by the Collateral Agent that the Exchanging
     Holders are unwilling to enter into the Exchange Agreement unless the
     Guarantee contemplated by this Section 2 is given by it.

     2.7. SUBROGATION. The Guarantor agrees that, until the Obligations are
indefeasibly paid in full, it will not exercise any right of reimbursement,
subrogation, contribution, offset or other claims against the Borrower or any
other Obligor arising by contract or operation of law in connection with any
payment made or required to be made by the Guarantor under this Agreement. After
the payment in full of the Obligations, the Guarantor shall be entitled to
exercise against the Borrower and the other Obligors all such rights of
reimbursement, subrogation, contribution and offset, and all such other claims,
to the fullest extent permitted by law.

     2.8. SUBORDINATION. The Guarantor covenants and agrees that all
Indebtedness, claims and liabilities now or hereafter owing by the Borrower or
any other Obligor to the Guarantor whether arising hereunder or otherwise are
subordinated to the prior payment in full of the Obligations and are so
subordinated as a claim against such Obligor or any of its assets, whether such
claim be in the ordinary course of business or in the event of voluntary or
involuntary liquidation, dissolution, insolvency or bankruptcy, so that no
payment with respect to any such Indebtedness, claim or liability will be made
or received while any Event of Default exists.

     2.9. FUTURE SUBSIDIARIES; FURTHER ASSURANCES. The Guarantor will from time
to time cause (a) any present Wholly Owned Subsidiary that is not a Guarantor
within 30 days after notice from the Collateral Agent or (b) any future Wholly
Owned Subsidiary within 30 days after any such Person becomes a Wholly Owned
Subsidiary, to join this Agreement as a Guarantor pursuant to a joinder
agreement in form and substance satisfactory to the Collateral Agent; PROVIDED,
HOWEVER, that in the event such a Wholly Owned Subsidiary is prohibited by any
valid law, statute, rule or regulation from guaranteeing the Obligations, or if
such a guarantee by any foreign Subsidiary would result in a repatriation of a
material amount of foreign earnings under the Code (including the "deemed
dividend" provisions of section 956 of the Code), (i) such guarantee will be
limited to the extent necessary to comply with such prohibition or to prevent
such repatriation of foreign earnings or (ii) if such limitation on the
guaranteed amount is not

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sufficient to avoid such prohibition or repatriation, the Borrower and its other
Subsidiaries will pledge the stock of such Wholly Owned Subsidiary (or as much
of such stock as may be pledged without resulting in such a repatriation) to the
Collateral Agent to secure the Obligations pursuant to a pledge agreement in
form and substance satisfactory to the Collateral Agent. The Guarantor will,
promptly upon the request of the Collateral Agent from time to time, execute,
acknowledge and deliver, and file and record, all such instruments, and take all
such action, as the Collateral Agent deems necessary or advisable to carry out
the intent and purpose of this Section 2.

3.   REPRESENTATIONS AND WARRANTIES. In order to induce the Exchanging Holders
to extend credit under the Exchange Agreement, the Guarantor represents and
warrants that:

     3.1. ORGANIZATION AND BUSINESS. The Guarantor is a duly organized and
validly existing corporation, in good standing under the laws of The
Commonwealth of Massachusetts, as applicable, with all power and authority,
corporate or otherwise, necessary (a) to enter into and perform this Agreement
and each other Credit Document to which it is a party and (b) to own its
properties and carry on the business now conducted or proposed to be conducted
by it. Certified copies of the Charter and By-laws of the Guarantor have been
previously delivered to the Collateral Agent and are correct and complete.

     3.2. AUTHORIZATION AND ENFORCEABILITY. The Guarantor has taken all
corporate action required to execute, deliver and perform this Agreement and
each other Credit Document to which it is a party. Each of this Agreement and
each other Credit Document to which the Guarantor is party constitutes the
legal, valid and binding obligation of the Guarantor, enforceable against the
Guarantor in accordance with its terms.

     3.3. NO LEGAL OBSTACLE TO AGREEMENTS. Neither the execution, delivery and
performance of this Agreement or any other Credit Document to which it is party,
nor the consummation of any transaction referred to in or contemplated by this
Agreement or any other Credit Document, has constituted or resulted, or will
constitute or result, in:

          (a)  Any breach or termination of the provisions of any agreement,
     instrument, deed or lease to which the Guarantor is a party or by which it
     is bound, or of the Charter or By-laws of the Guarantor; or

          (b)  The violation of any law, statute, judgment, decree or
     governmental order, rule or regulation applicable to the Guarantor.

No approval, authorization or other action by, or declaration to or filing with,
any governmental or administrative authority or any other Person is required to
be obtained or made by the Guarantor in connection with the execution, delivery
and performance of this Agreement or any other Credit Document to which it is
party or the transactions contemplated hereby or thereby.

     3.4. LITIGATION. Except as disclosed in the SEC Reports, no litigation, at
law or in equity, or any proceeding before any court, board or other
governmental or administrative

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agency or any arbitrator is pending or, to the knowledge of the Guarantor,
threatened which may involve any material risk of any final judgment, order or
liability which, after giving effect to any applicable insurance, has resulted,
or creates a material risk of resulting, in any material adverse change in the
Guarantor's business, assets, financial condition, income or prospects or which
seeks to enjoin the consummation, or which questions the validity, of any of the
transactions contemplated by this Agreement or any other Credit Document. No
judgment, decree or order of any court, board or other governmental or
administrative agency or any arbitrator has been issued against or binds the
Guarantor which has resulted, or creates a material risk of resulting, in any
material adverse change in the Guarantor's business, assets, financial
condition, income or prospects.

4.   SUCCESSORS AND ASSIGNS. The provisions of this Agreement shall inure to the
benefit of the Holders and their successors and assigns and shall be binding
upon the Guarantor and its respective successors and assigns. The Guarantor may
not assign its rights or obligations under this Agreement without the written
consent of the Collateral Agent.

5.   NOTICES. Any notice or other communication in connection with this
Agreement shall be deemed to be given if given in writing (including telex,
telecopy or similar teletransmission) addressed as provided below (or to the
addressee at such other address as the addressee shall have specified by notice
actually received by the addressor), and if either (a) actually delivered in
fully legible form to such address (evidenced in the case of a telex by receipt
of the correct answerback) or (b) in the case of a letter, five business days
shall have elapsed after the same shall have been deposited in the United States
mails, with first-class postage prepaid and registered or certified.

     If to the Guarantor, to it in care of iBasis, Inc., 20 Second Avenue,
Burlington, MA 01803, to the attention of its chief financial officer.

     If to the Collateral Agent, to it at its address specified in or pursuant
to section 13 of the Exchange Agreement.

6.   REIMBURSEMENT OF EXPENSES. Subject to the terms of the Fee Letter (as such
term is defined in the Exchange Agreement) and the Exchange Agreement, the
Guarantor shall promptly pay on demand all reasonable expenses of the Collateral
Agent and the Exchanging Holders (including reasonable attorney fees and
expenses) in connection with the preparation of this Agreement, operations
hereunder and enforcement and collection hereof, whether before or after
bankruptcy or similar proceedings (and whether or not allowed as a claim
therein).

7.   VENUE; SERVICE OF PROCESS.  Each Guarantor:

          (a)  Irrevocably submits to the nonexclusive jurisdiction of the state
     courts of the Commonwealth of Massachusetts and to the nonexclusive
     jurisdiction of the United States District Court for the District of
     Massachusetts for the purpose of any suit, action or other proceeding
     arising out of or based upon this Agreement or any other Credit Document or
     the subject matter hereof or thereof;

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          (b)  Waives to the extent not prohibited by applicable law, and agrees
     not to assert, by way of motion, as a defense or otherwise, in any such
     proceeding brought in any of the above-named courts, any claim that it is
     not subject personally to the jurisdiction of such court, that its property
     is exempt or immune from attachment or execution, that such proceeding is
     brought in an inconvenient forum, that the venue of any such proceeding is
     improper, or that this Agreement or any other Credit Document, or the
     subject matter hereof or thereof, may not be enforced in or by such court;

          (c)  Consents to service of process in any such proceeding in any
     manner permitted by law and agrees that service of process by registered or
     certified mail, return receipt requested, at its address specified in or
     pursuant to Section 5 is reasonably calculated to give actual notice; and

          (d)  Waives to the extent not prohibited by applicable law that cannot
     be waived any right it may have to claim or recover in any such proceeding
     any special, exemplary, punitive or consequential damages.

8.   WAIVER OF JURY TRIAL. TO THE EXTENT NOT PROHIBITED BY APPLICABLE LAW WHICH
CANNOT BE WAIVED, EACH OF THE COLLATERAL AGENT AND EACH GUARANTOR WAIVES, AND
COVENANTS THAT IT WILL NOT ASSERT (WHETHER AS PLAINTIFF, DEFENDANT OR
OTHERWISE), ANY RIGHT TO TRIAL BY JURY IN ANY FORUM IN RESPECT OF ANY ISSUE,
CLAIM, DEMAND OR ACTION ARISING OUT OF OR BASED UPON THIS AGREEMENT, THE
SECURITIES EXCHANGE AGREEMENT OR ANY OTHER CREDIT DOCUMENT OR THE SUBJECT MATTER
HEREOF OR THEREOF OR ANY OBLIGATION OR IN ANY WAY CONNECTED WITH THE DEALINGS OF
THE COLLATERAL AGENT OR THE GUARANTOR IN CONNECTION WITH ANY OF THE ABOVE, IN
EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING AND WHETHER IN CONTRACT OR
TORT OR OTHERWISE. Each Guarantor and the Collateral Agent acknowledges that the
provisions of this Section constitute a material inducement upon which each
party has relied, is relying and will rely in entering into the Exchange
Agreement and any other Credit Document, and that it has reviewed the provisions
of this Section with its counsel. The Collateral Agent or the Guarantor may file
an original counterpart or a copy of this Section with any court as written
evidence of the consent of the Collateral Agent and the Guarantor to the waiver
of the right to trial by jury.

9.   GENERAL. All covenants, agreements, representations and warranties made in
this Agreement or any other Credit Document or in certificates delivered
pursuant hereto or thereto shall be deemed to have been relied on by each
Exchanging Holder, notwithstanding any investigation made by the Collateral
Agent on its behalf, and shall survive the execution and delivery to the
Exchanging Holders and the Holders hereof and thereof. The invalidity or
unenforceability of any provision hereof shall not affect the validity or
enforceability of any other provision hereof, and any invalid or unenforceable
provision shall be modified so as to be enforced to the maximum extent of its
validity or enforceability. The headings in this Agreement

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are for convenience of reference only and shall not limit, alter or otherwise
affect the meaning hereof. This Agreement and the other Credit Documents
constitute the entire understanding of the parties with respect to the subject
matter hereof and thereof and supersede all prior and current understandings and
agreements, whether written or oral. This Agreement is a Credit Document and may
be executed in any number of counterparts, which together shall constitute one
instrument. This Agreement shall be governed by, and shall be construed and
enforced in accordance with, the laws of The Commonwealth of Massachusetts,
without regard to the principles of conflicts of laws. Each beneficial holder of
the Obligations shall be entitled to the benefits of a Holder under this
Agreement.

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     Each of the undersigned has caused this Agreement to be executed and
delivered by its duly authorized officer as an agreement under seal as of the
date first written above.


                                       iBASIS SECURITIES CORPORATION


                                       By:   /s/ Gordon VanderBrug
                                          --------------------------------------
                                          Title:  Executive Vice President


                                       U.S. BANK NATIONAL ASSOCIATION,
                                       as Collateral Agent


                                       By:   /s/ John A. Brennan
                                          ---------------------------------
                                          Title: Trust Officer