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                                                                   Exhibit 10.66

                                                                  EXECUTION COPY

                             INTERCREDITOR AGREEMENT

     This Intercreditor Agreement (the "Intercreditor Agreement" or the
"Agreement") is made as of June 18, 2004, by and among (a) the undersigned
"Creditors" signatory hereto and all subsequent holders of the Notes (as defined
in the Indenture referred to below) or beneficial interests therein
(collectively, the "Creditors"); (b) SILICON VALLEY BANK, a California-chartered
bank, with its principal place of business at 3003 Tasman Drive, Santa Clara,
California 95054 and with a loan production office located at 2221 Washington
Street, Suite 200, Newton, Massachusetts 02462, doing business under the name
"Silicon Valley East" ("Bank"), (c) IBASIS, INC., a Delaware corporation (the
"Company"), IBASIS GLOBAL, INC., a Delaware corporation ("Global"), IBASIS
HOLDINGS, INC., a Delaware corporation ("Holdings"), and IBASIS SECURITIES
CORPORATION, a Massachusetts corporation ("Securities", and, collectively with
the Company, Global and Holdings, the "Obligors"), and (d) THE BANK OF NEW YORK,
in its capacity as Collateral Agent (as such term is defined in the Indenture
referred to below) and THE BANK OF NEW YORK, in its capacity as Trustee (as such
term is defined in the Indenture referred to below).

                                    RECITALS

     A.   The Obligors have requested and/or obtained certain loans or other
credit accommodations from Bank to Obligors which are or may be from time to
time secured by assets and property of Obligors.

     B.   Pursuant to the terms of that certain Indenture dated June 18, 2004 by
and among the Obligors and the Trustee (as the same may be amended, restated,
modified and/or supplemented from time to time, the "Indenture"), the Creditors
have extended loans or other credit accommodations to the Company or may acquire
Notes (as such term is defined in the Indenture) from other Creditors and the
Company has issued the Notes (as defined in the Indenture) to the Creditors in
accordance with the terms thereof.

     C.   Pursuant to the terms of the Indenture, Global and Securities have
guaranteed all of the Company's obligations owing to the Creditors, the
Collateral Agent and the Trustee under the Indenture and the Notes.

     D.   In order to induce Bank to continue to extend credit to Obligors and,
at any time or from time to time, at Bank's option, to make such further loans,
extensions of credit, or other accommodations to or for the account of any
Obligor, or to purchase or extend credit upon any instrument or writing in
respect of which an Obligor may be liable in any capacity, or to grant such
renewals or extension of any such loan, extension of credit, purchase, or other
accommodation as Bank may deem advisable, the Creditors and the Collateral Agent
are willing to subordinate: (i) all of the Obligors' indebtedness and
obligations to the Creditors pursuant to (a) the Indenture, including, without
limitation, the Notes issued under the Indenture and the guarantee obligations
of Global and Securities contained in the Indenture and (b) each additional Note
issued under the Indenture (all of Obligors' indebtedness and obligations under
the Indenture and Notes being hereinafter collectively referred to as the
"Subordinated Debt") to all of Obligors' indebtedness and obligations to Bank
other than (1) any obligations and indebtedness owing to the Bank under any of
the 6 3/4% Convertible Subordinated Notes due

                                       -1-
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2009 (as defined in the Indenture) or the 5 3/4% Convertible Subordinated Notes
due 2005 (as defined in the Indenture) (collectively, the "Junior Notes"); (2)
any obligations and indebtedness owing to the Bank pursuant to any instrument,
document or agreement which specifically provides therein that the indebtedness
thereunder is junior in right of payment to the Subordinated Debt (the "Express
Junior Debt"); or (3) any obligations and indebtedness owing to the Bank
pursuant to any instrument, document or agreement which specifically provides
therein that the indebtedness thereunder is pari passu in right of payment to
the Subordinated Debt (the "Express Pari Passu Debt" and, collectively with the
Junior Notes and the Express Junior Debt, the "Junior Debt")and (ii) all of the
Collateral Agent's security interests, if any, to all of Bank's security
interests in the Obligors' property.

NOW, THEREFORE, THE PARTIES AGREE AS FOLLOWS:

1.   The Creditors and the Collateral Agent hereby subordinates to Bank any
     security interest or lien that the Collateral Agent may have for the
     benefit of the Creditors, the Trustee or the Collateral Agent in any
     property of Obligors. Notwithstanding the respective dates of attachment or
     perfection of the security interest of the Collateral Agent and the
     security interest of Bank, the security interest of Bank in the Collateral
     (as defined in a certain Amended and Restated Loan and Security Agreement
     (the "Loan Agreement") among the Company, Global and Bank dated as of
     December 29, 2003 and as also defined in a certain Security Agreement
     between Securities and Bank dated December 29, 2003 and in a certain
     Security Agreement between Global and Bank dated December 29, 2003, as each
     may be amended from time to time), shall at all times be senior to the
     security interest granted to the Collateral Agent for the benefit of the
     Creditors, the Trustee or the Collateral Agent under the Security Documents
     (as defined in the Indenture).

2.   All Subordinated Debt is subordinated in right of payment to all
     obligations of Obligors to Bank, other than any Junior Debt, now existing
     or hereafter arising, together with all costs of collecting such
     obligations (including attorneys' fees), including, without limitation, all
     interest accruing after the commencement by or against any Obligor of any
     bankruptcy, reorganization or similar proceeding, and all obligations under
     the Loan Agreement (the "Senior Debt").

3.   Except as otherwise expressly provided herein, the Creditors will not
     demand or receive from any Obligor (and Obligor will not pay to the
     Creditors (or the Trustee on behalf of the Creditors)) all or any part of
     the Subordinated Debt, by way of payment, prepayment, setoff, lawsuit or
     otherwise, nor will the Collateral Agent exercise any remedy with respect
     to the Collateral, nor will the Creditors (or the Trustee on behalf of the
     Creditors) accelerate the Subordinated Debt, or commence, or cause to
     commence, prosecute or participate in any administrative, legal or
     equitable action against any Obligor, until such time as both (i) the
     Senior Debt is fully paid in cash and (ii) Bank has no commitment or
     obligation to lend any further funds to Obligors. Nothing in the foregoing
     paragraph shall prohibit the Creditors from converting all or any part of
     the Subordinated Debt into equity securities of any Obligor.

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4.   Subject to Section 5, the Company shall be permitted to make, and the
     Creditors shall be permitted to accept or receive the following permitted
     payments ("Permitted Payments"): (i) scheduled payments of interest when
     due pursuant to the terms of the Subordinated Debt, (ii) payment in full of
     principal outstanding under the Subordinated Debt at the later of (x) the
     maturity date of the Subordinated Debt or (y) June 18, 2007 and (iii) other
     payments specifically consented to in writing by Bank prior to the making
     of such payment. In accordance with Section 3 above, the Company
     acknowledges that it cannot voluntarily prepay the entire indebtedness or
     any portion thereof due the Creditors nor make any payments other than
     Permitted Payments, without Bank's prior written consent and the Creditors
     (and the Trustee on behalf of the Creditors) acknowledge that they will not
     accept any payment, other than a Permitted Payment, without Bank's prior
     written consent.

5.   i.     If, after an Event of Default, as defined in the Indenture, has
     occurred, the Creditors, the Trustee or the Collateral Agent desire to
     exercise remedies, the Creditors shall provide Bank with a written notice
     (the "Creditors' Notice") that there has occurred such an Event of Default
     under the Subordinated Debt. Bank shall respond to such notice to the
     Trustee, the Collateral Agent and to the Creditors at the addresses set
     forth in their notice, within fifteen (15) days after receipt of the
     Creditors' Notice and Bank shall elect at its sole option to: (1) deliver a
     Blockage Notice (as defined below) to the Creditors, the Trustee and the
     Collateral Agent or (2) deliver a notice that the Creditors, the Trustee
     and/or the Collateral Agent may exercise remedies provided that the
     Creditors, the Trustee or the Collateral Agent, as the case may be, shall
     remit the proceeds of all Collateral to Bank until such time as the Senior
     Debt is paid in full. If the Bank shall fail to respond to the Creditors'
     Notice, in accordance with the preceding sentence, within fifteen (15) days
     after receipt of the Creditors' Notice, the Creditors, the Trustee and/or
     the Collateral Agent, as the case may be, may exercise their rights and
     remedies provided that the Creditors, the Trustee or the Collateral Agent,
     as the case may be, shall remit to Bank all payments, distributions and or
     other proceeds received by the Creditors, the Trustee or the Collateral
     Agent, as the case may be, from the Obligors or with respect to the
     Collateral until such time as the Senior Debt is paid full.

     ii.    If, at any time, there is an Event of Default (as defined in the
     Loan Agreement) under the Senior Debt, Bank may deliver written notice to
     the Trustee, the Collateral Agent and to the Creditors that there is such
     an Event of Default under the Senior Debt (a "Blockage Notice") and neither
     the Trustee, the Creditors nor the Collateral Agent shall be entitled to
     accept or receive any payments on the Subordinated Debt (including, without
     limitation, any Permitted Payments) until the earlier of: (1) the Senior
     Debt is paid in full and Bank's commitment to lend has been terminated, (2)
     Bank rescinds the Blockage Notice or the Event of Default has been cured or
     waived by Bank in writing or (3) the end of the Blockage Period. The
     "Blockage Period" shall commence at the time the Blockage Notice is
     delivered to the Trustee, the Collateral Agent and the Creditors and expire
     on the earlier to occur of the following: (1) (x) 180 days following the
     delivery of the Blockage Notice for non-payment Events of Default under the
     Senior Debt or

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     (y) indefinitely for all payment Events of Default under the Senior Debt;
     PROVIDED THAT if, with respect to a Blockage Period based on non-payment
     defaults under the Senior Debt, prior to the expiration of such 180-day
     period Bank has commenced a judicial proceeding or a non-judicial action to
     collect or enforce the Senior Debt or exercised rights with respect to the
     Collateral and Bank continues to diligently pursue same, or a case or
     proceeding by or against the Obligors is commenced under the federal
     Bankruptcy Code or any other insolvency law, then such period shall be
     extended during the continuation of such proceedings and actions until the
     payment in cash or other property or securities in the full amount of the
     allowed claim of Bank under the Senior Debt; or (2) Bank's written consent
     to the termination of the Blockage Period. With respect to non-payment
     defaults under the Senior Debt, in no event shall the Blockage Period
     during any period of 365 consecutive days exceed 180 days in the aggregate,
     whether pursuant to one Blockage Notice or multiple Blockage Notices.

6.   The Creditors, the Trustee and the Collateral Agent, as the case may be,
     shall promptly deliver to Bank in the form received (except for endorsement
     or assignment by the Creditors, the Trustee or the Collateral Agent, as the
     case may be, where required by Bank) for application to the Senior Debt any
     payment, distribution, security or proceeds received by the Creditors, the
     Trustee or the Collateral Agent, as the case may be, with respect to the
     Subordinated Debt other than in accordance with this Intercreditor
     Agreement (other than equity securities or debt subordinated to the Senior
     Debt on the same terms as the Subordinated Debt).

7.   In the event of any Obligor's insolvency, reorganization or any case or
     proceeding under any bankruptcy or insolvency law or laws relating to the
     relief of debtors, these provisions shall remain in full force and effect,
     and Bank's claims against such Obligor and the estate of such Obligor shall
     be paid in full before any payment is made to the Creditors.

8.   Until the Senior Debt is fully paid in cash, and Bank's obligation to lend
     any funds to Obligor has been terminated, the Creditors hereby authorize
     Bank, as Creditors' attorney-in-fact, to file in any bankruptcy, insolvency
     or similar proceeding involving the Obligors the appropriate claim or
     claims in respect of the Subordinated Debt on behalf of the Creditors if
     the Creditors do not do so prior to 15 days before the expiration of the
     time to file claims in such proceeding and if Bank elects, in its sole
     discretion, to file such claim or claims.

9.   No amendment of the documents evidencing or relating to the Subordinated
     Debt shall directly or indirectly modify the provisions of this
     Intercreditor Agreement in any manner which might terminate or impair the
     subordination of the Subordinated Debt or the subordination of the security
     interest or lien that the Collateral Agent may have in any property of
     Borrower. In addition, such instruments shall not be, in any event, amended
     to (i) increase the rate of interest with respect to the Subordinated Debt,
     or (ii) accelerate the payment of the principal or interest or any other
     portion of the Subordinated Debt.

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10.  If, at any time after payment in full of the Senior Debt any payments of
     the Senior Debt must be disgorged by Bank for any reason (including,
     without limitation, the bankruptcy of an Obligor), this Intercreditor
     Agreement and the relative rights and priorities set forth herein shall be
     reinstated as to all such disgorged payments as though such payments had
     not been made and the Creditors shall immediately pay over to Bank all
     payments received with respect to the Subordinated Debt to the extent that
     such payments would have been prohibited hereunder. At any time and from
     time to time, without notice to the Creditors, Bank may take such actions
     with respect to the Senior Debt as Bank, in its sole discretion, may deem
     appropriate, including, without limitation, terminating advances to an
     Obligor, increasing the principal amount, extending the time of payment,
     increasing applicable interest rates, renewing, compromising or otherwise
     amending the terms of any documents affecting the Senior Debt and any
     collateral securing the Senior Debt, and enforcing or failing to enforce
     any rights against any Obligor or any other person. No such action or
     inaction shall impair or otherwise affect Bank's rights hereunder.

11.  This Intercreditor Agreement shall bind any successors or assignees of the
     Creditors, the Trustee and the Collateral Agent, including any transferees
     of Notes or beneficial interests in Notes, and shall benefit any successors
     or assigns of Bank. This Intercreditor Agreement shall remain effective
     until terminated in writing by Bank. This Intercreditor Agreement is solely
     for the benefit of the Creditors, the Trustee, the Collateral Agent and
     Bank and not for the benefit of any Obligor or any other party. The
     Creditors, the Trustee and the Collateral Agent further agree that if any
     Obligor refinances all or any portion of the Senior Debt with a new lender,
     and if Bank or any Obligor makes a request of the Creditors, the Trustee
     and the Collateral Agent, the Creditors, the Collateral Agent and the
     Trustee shall agree to enter into a new intercreditor agreement with the
     new lender on substantially the terms and conditions of this Intercreditor
     Agreement, and such intercreditor agreement shall be deemed to be in full
     force and effect, regardless of whether or not executed by such Creditors,
     the Trustee and the Collateral Agent from and after the earlier of (x) such
     request, or (y) the consummation of such refinancing.

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

13.  This Intercreditor Agreement shall be governed by and construed in
     accordance with the laws of the Commonwealth of Massachusetts, without
     giving effect to conflicts of laws principles, except with respect to the
     rights, duties and liabilities of the Trustee and the Collateral Agent,
     which shall be governed by and construed in accordance with the laws of the
     State of New York. The Creditors, the Trustee, the Collateral Agent and
     Bank submit to the non-exclusive jurisdiction of the state and federal
     courts located in Boston, Massachusetts in any action, suit, or proceeding
     of any kind, against it which arises out of or by reason of this
     Intercreditor Agreement; provided, however, that if for any reason Bank
     cannot avail itself of the Courts of The Commonwealth of Massachusetts, the
     Creditors, the Trustee and the Collateral Agent accept jurisdiction of the
     Courts and venue in Santa Clara County, California. THE CREDITORS, THE
     TRUSTEE, THE

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     COLLATERAL AGENT AND BANK WAIVE THEIR RESPECTIVE RIGHTS TO A JURY TRIAL OF
     ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS
     INTERCREDITOR AGREEMENT OR ANY OF THE TRANSACTIONS CONTEMPLATED HEREIN.

14.  This Intercreditor Agreement represents the entire agreement with respect
     to the subject matter hereof, and supersedes all prior negotiations,
     agreements and commitments. The Creditors are not relying on any
     representations by Bank or Obligor in entering into this Intercreditor
     Agreement, and the Creditors have kept and will continue to keep themselves
     fully apprised of the financial and other condition of Obligors. Subject to
     the last sentence of paragraph 12 above, this Intercreditor Agreement may
     be amended only by written instrument signed by the Creditors, the Trustee,
     the Collateral Agent and Bank.

15.  In the event that Bank is holding original chattel paper, documents,
     instruments, or investment property of any Obligor, Bank hereby
     acknowledges that it is holding such Collateral for the benefit of the
     Collateral Agent (for the benefit of the Creditors, the Trustee and the
     Collateral Agent) as an additional secured party, as well as holding such
     Collateral for its own account, subject to the relative priorities set
     forth herein. The Collateral Agent and the Creditors hereby acknowledge and
     agree that Bank has no fiduciary duty, duty of safekeeping, duty as bailee
     or any other duty to the Collateral Agent and the Creditors with regard to
     such Collateral. Bank hereby agrees to deliver such original Collateral to
     the Collateral Agent upon payment in full of all Senior Debt and
     termination of this Intercreditor Agreement.

16.  (i) The Collateral Agent, the Trustee and each Creditor hereby agrees that
     (a) any and all rights and powers of the Collateral Agent under or pursuant
     to the Indenture and any of the Security Documents (as defined in the
     Indenture) shall be subject to the terms of this Intercreditor Agreement,
     and (b) the Collateral Agent shall not knowingly take, and neither the
     Trustee nor the Creditors shall instruct or direct the Collateral Agent to
     take, any action that would be in violation of the terms hereof.

     (ii)   The Collateral Agent is entering into this Intercreditor Agreement
solely in its capacity as Collateral Agent under the Indenture and the Security
Documents, and not otherwise. The Collateral Agent shall have no any liability
or responsibility for the actions or omissions of the Trustee or any Creditor,
or for the Trustee's or any Creditor's compliance with (or failure to comply
with) the terms of this Intercreditor Agreement. The Collateral Agent shall not
have individual liability to the Bank if it shall mistakenly pay over or
distribute to any Creditor, the Trustee or any Obligor any amounts to which the
Bank is entitled under this Intercreditor Agreement, so long as the Collateral
Agent is acting in good faith. Nothing in this Intercreditor Agreement shall be
construed to subordinate or apply to any payment of fees or expenses to the
Collateral Agent to which it is entitled.

     (iii)  In entering into this Intercreditor Agreement, and in performing or
observing any of the terms of this Intercreditor Agreement, and otherwise in
respect of any matter arising under or in respect of this Intercreditor
Agreement, the Collateral Agent shall enjoy and shall be protected by each of
the rights, immunities, indemnities and other protections set forth in the
Indenture, the

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Security Documents, the Collateral Agency/Intercreditor Agreement (as such term
is defined in the "Indenture") and any other agreement relating thereto; and any
obligations, duties or liabilities to which the Collateral Agent may be or
become subject under or in respect of this Intercreditor Agreement shall be
subject to and limited by the terms of the Indenture, the Security Documents,
the Collateral Agency/Intercreditor Agreement and any other agreement relating
thereto. Subject to the other provisions of this Section 16, in no event shall
the Collateral Agent have any liability hereunder that it would not have, nor
shall the Collateral Agent be obligated to take any action hereunder that it
would not be required to take, under the terms of the Indenture, the Security
Documents and any other agreement relating thereto. The Collateral Agent has no
responsibility for the terms of this Intercreditor Agreement or its sufficiency
for any purpose.

     (iv)   The Trustee is entering into this Intercreditor Agreement solely in
its capacity as Trustee under the Indenture, and not otherwise. The Trustee
shall have no any liability or responsibility for the actions or omissions of
the Collateral Agent or any Creditor, or for the Collateral Agent's or any
Creditor's compliance with (or failure to comply with) the terms of this
Intercreditor Agreement. The Trustee shall not have individual liability to the
Bank if it shall mistakenly pay over or distribute to any Creditor (or any
Obligor) any amounts to which the Bank is entitled under this Intercreditor
Agreement, so long as the Trustee is acting in good faith. Nothing in this
Intercreditor Agreement shall be construed to subordinate or apply to any
payment of fees or expenses to the Trustee to which it is entitled.

     (v)    In entering into this Intercreditor Agreement, and in performing or
observing any of the terms of this Intercreditor Agreement, and otherwise in
respect of any matter arising under or in respect of this Intercreditor
Agreement, the Trustee shall enjoy and shall be protected by each of the rights,
immunities, indemnities and other protections set forth in the Indenture; and
any obligations, duties or liabilities to which the Trustee may be or become
subject under or in respect of this Intercreditor Agreement shall be subject to
and limited by the terms of the Indenture. Subject to the other provisions of
this Section 16, in no event shall the Trustee have any liability hereunder that
it would not have, nor shall the Trustee be obligated to take any action
hereunder that it would not be required to take, under the terms of the
Indenture. The Trustee has no responsibility for the terms of this Intercreditor
Agreement or its sufficiency for any purpose.

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          IN WITNESS WHEREOF, the undersigned have executed this Intercreditor
Agreement as of the date first above written.

                               "Bank"

                               SILICON VALLEY BANK


                               By:    /s/ Authorized Signatory
                                  ----------------------------------------------


                               "Collateral Agent"

                               THE BANK OF NEW YORK


                               By:    /s/ Geovanni Barris
                                  ----------------------------------------------

                               Title: Vice President
                                     -------------------------------------------


                               "Trustee"

                               THE BANK OF NEW YORK


                               By:    /s/ Geovanni Barris
                                  ----------------------------------------------

                               Title: Vice President
                                     -------------------------------------------

                                       -8-
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                               "Creditors"

                               GREYWOLF CAPITAL OVERSEAS FUND


                               By: /s/ William Troy
                                   ---------------------------------------------

                               Title:  Chief Operating Officer
                                     -------------------------------------------


                               GREYWOLF CAPITAL PARTNERS II LP


                               By: /s/ William Troy
                                   ---------------------------------------------

                               Title:  Chief Operating Officer
                                     -------------------------------------------


                               TEJAS SECURITIES GROUP, INC.
                               401K PLAN & TRUST
                               JOHN GORMAN TTEE UAD 1/1/96 FBO JOHN J GORMAN


                               By: /s/ John Gorman
                                   ---------------------------------------------

                               Title:  Trustee
                                     -------------------------------------------


                               SCHOTTENFELD QUALIFIED ASSOCIATES


                               By: /s/ Richard Schottenfeld
                                   ---------------------------------------------

                               Title:  Managing Member of the General Partner
                                     -------------------------------------------

                                       -9-
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                               LC CAPITAL MASTER FUND, LTD.


                               By: /s Steven Lampe
                                   ---------------------------------------------

                               Title:  Managing Member of the Advisor
                                     -------------------------------------------


                               SINGER CHILDREN'S MANAGEMENT TRUST


                               By: /s/ Gary Singer
                                   ---------------------------------------------

                               Title:  Investment Advisor
                                     -------------------------------------------


                               LOEB PARTNERS CORP.


                               By /s/ Robert Grubin
                                  ----------------------------------------------

                               Title:  Vice President
                                     -------------------------------------------


                               JMG TRITON OFFSHORE FUND LIMITED

                               By its Investment Manager, Pacific Assets
                               Management, LLC


                               By /s/ Jonathan Glaser
                                  ----------------------------------------------

                               Title:  Member Manager
                                     -------------------------------------------

                                      -10-
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                               JMG CAPITAL PARTNERS

                               By its General Partner, JMG Capital Management,
                               LLC


                               By /s/ Jonathan Glaser
                                  ----------------------------------------------

                               Title:  Member Manager
                                     -------------------------------------------


                               WINDWARD CAPITAL, L.P.


                               By: /s/ Kim Emerson Morris
                                   ---------------------------------------------

                               Title:  Portfolio Manager
                                     -------------------------------------------

                                      -11-
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The undersigned approves of the terms of this Intercreditor Agreement.

"Obligors"

IBASIS, INC.


By:/s/ Gordon J. Vanderbrug
   ----------------------------------------------------------

Title: Executive Vice President
       ------------------------------------------------------

IBASIS GLOBAL, INC.


By: /s/ Richard Tennant
    ---------------------------------------------------------

Title: Vice President, Finance and Chief Financial Officer
       ------------------------------------------------------

IBASIS SECURITIES CORPORATION.


By:/s/ Gordon J. Vanderbrug
   ----------------------------------------------------------

Title: Executive Vice President
       ------------------------------------------------------

                                      -12-
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IBASIS HOLDINGS, INC.


By: /s/ Ofer Gneezy
   ----------------------------------------------------------

Title: President
      -------------------------------------------------------

                                      -13-