<Page>

                                                                     EXHIBIT 4.6

                             SUBORDINATION AGREEMENT

     This Subordination Agreement is made as of January 30, 2003, by and
between the undersigned "Creditors" signatory hereto and all subsequent holders
of the Notes (as defined herein) or beneficial interests therein (collectively,
the "Creditors") and 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"), and for purposes of Section 17 below, U.S. Bank National Association,
as Collateral Agent and as Fiscal Agent, respectively, under the Exchange
Agreement and the Fiscal Agency Agreement referred to below (collectively, in
such capacities, the "Agent").

                                    RECITALS

     A. IBASIS, INC., a Delaware corporation, IBASIS GLOBAL, INC., a Delaware
corporation and IBASIS SECURITIES CORPORATION, a Massachusetts corporation
(collectively, "Borrower") has requested and/or obtained certain loans or other
credit accommodations from Bank to Borrower which are or may be from time to
time secured by assets and property of Borrower.

     B. The Creditors have extended loans or other credit accommodations to
Borrower, and/or may extend loans or other credit accommodations to Borrower
from time to time or may acquire Notes from other Creditors.

     C. In order to induce Bank to extend credit to Borrower 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 Borrower, or to
purchase or extend credit upon any instrument or writing in respect of which
Borrower 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 are willing to subordinate: (i) all of
Borrower's indebtedness and obligations to the Creditors pursuant to (a) those
notes issued in connection with the Securities Exchange Agreement (the "Exchange
Agreement") among the Borrower, the investors signatory thereto (the
"Investors") and U.S. Bank National Association as Collateral Agent and Fiscal
Agent for the Investors, dated as of January ___, 2003 (the "Symphony Notes")
and (b) each additional note issued pursuant to a "Permitted Exchange" (as such
term is defined in the Exchange Agreement) (the "Additional Notes" and, together
with the Symphony Notes, the "Notes") (all of Borrower's indebtedness and
obligations under the Notes being hereinafter collectively referred to as the
"Subordinated Debt") to all of Borrower's indebtedness and obligations to Bank;
and (ii) all of the Creditors' security interests, if any, to all of Bank's
security interests in the Borrower's property.

     NOW, THEREFORE, THE PARTIES AGREE AS FOLLOWS:

     1. The Creditors subordinate to Bank any security interest or lien that the
Creditors may have in any property of Borrower. Notwithstanding the respective
dates of attachment or perfection of the security interest of the Creditors and
the security interest of Bank, the security interest of Bank in the Collateral
(the "Collateral"), as defined in a certain Loan and Security Agreement (the
"Loan Agreement") among iBasis, Inc., iBasis Global, Inc. and Bank dated as of
December 30, 2002 and as also defined in a certain Security Agreement between
iBasis Securities Corporation and Bank dated December 30, 2002, as each may be
amended from time to time, shall at all times be senior to the security interest
of the Creditors.

     2. All Subordinated Debt is subordinated in right of payment to all
obligations of Borrower to Bank 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
Borrower 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 Borrower (and Borrower will not pay to the Creditors) all
or any part of the Subordinated Debt, by way of payment, prepayment, setoff,
lawsuit or otherwise, nor will the Creditors exercise any remedy with respect to
the Collateral, nor will the Creditors accelerate the Subordinated Debt, or
commence, or cause to commence, prosecute or participate in any administrative,
legal or equitable action against Borrower, 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

<Page>

her funds to Borrower. Nothing in the foregoing paragraph shall prohibit the
Creditors from converting all or any part of the Subordinated Debt into equity
securities of Borrower.

     4. Subject to Section 5, Borrower 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) January 15, 2005 and (iii) other
payments specifically consented to in writing by Bank prior to the making of
such payment. In accordance with Section 3 above, Borrower 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 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 under the Subordinated Debt, the
     Creditors desire to exercise remedies, the Creditors shall provide Bank
     with a written notice (the "Creditors' Notice") that there has occurred an
     event of default under the Subordinated Debt. Bank shall respond to such
     notice to the Fiscal 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 or (2) deliver a notice that the
     Creditors may exercise remedies provided that the Creditors shall remit the
     proceeds of all Collateral to Bank until 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 may exercise their rights and remedies
     provided that the Creditors shall remit to Bank all payments, distributions
     and or other proceeds received by the Creditors from the Borrower or with
     respect to the Collateral until the Senior Debt is paid full.

          (ii) If, at any time, there is an Event of Default under the Senior
     Debt, Bank may deliver written notice to the Fiscal Agent and to the
     Creditors that there is an Event of Default under the Senior Debt (a
     "Blockage Notice") and the Creditors shall not 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 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 (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 Borrower 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 shall promptly deliver to Bank in the form received
(except for endorsement or assignment by the Creditors where required by Bank)
for application to the Senior Debt any payment, distribution, security or
proceeds received by the Creditors with respect to the Subordinated Debt other
than in accordance with this 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 Borrower'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 Borrower and the estate of Borrower shall be paid in full before
any payment is made to the Creditors.

<Page>

     8. Until the Senior Debt is fully paid in cash, and Bank's obligation to
lend any funds to Borrower has been terminated, the Creditors hereby authorize
Bank, as Creditors' attorney-in-fact, to file in any bankruptcy, insolvency or
similar proceeding involving Borrower 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. The Creditors shall immediately affix a legend to each of the Notes and
all other instruments evidencing the Subordinated Debt stating that the Notes
and such other instruments are subject to the terms of this Agreement. By the
execution of this Agreement, the Creditors hereby authorize Bank to amend any
financing statements filed by the Creditors against Borrower as follows: "In
accordance with a certain Subordination Agreement by and among the Secured
Party, the Debtor and Silicon Valley Bank, the Secured Party has subordinated
any security interest or lien that Secured Party may have in any property of the
Debtor to the security interest of Silicon Valley Bank in all assets of the
Debtor, notwithstanding the respective dates of attachment or perfection of the
security interest of the Secured Party and Silicon Valley Bank."

     10. No amendment of the documents evidencing or relating to the
Subordinated Debt shall directly or indirectly modify the provisions of this
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
Creditors 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.

     11. 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 Borrower), this 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 Borrower, 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 Borrower or any other person. No such action or inaction shall
impair or otherwise affect Bank's rights hereunder.

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

     13. This 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.

     14. This 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. The Creditors 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 Agreement; provided, however, that if for any reason Bank
cannot avail itself of the Courts of The Commonwealth of Massachusetts, the
Creditors accept jurisdiction of the Courts and venue in Santa Clara County,
California. THE CREDITORS AND BANK WAIVE THEIR RESPECTIVE RIGHTS TO A JURY TRIAL
OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS AGREEMENT OR
ANY OF THE TRANSACTIONS CONTEMPLATED HEREIN.

     15. This 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
Borrower in entering

                                       -3-
<Page>

into this Agreement, and the Creditors have kept and will continue to keep
themselves fully apprised of the financial and other condition of Borrower.
Subject to the last sentence of paragraph 12 above, this Agreement may be
amended only by written instrument signed by the Creditors and Bank.

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

     17. (i) The Collateral Agent and each Creditor hereby agrees that (a) any
and all rights and powers of the Collateral Agent under or pursuant to the
Securities Exchange Agreement dated as of January __, 2003 by and among the
Borrower, the Guarantors defined therein, the Creditors and the Collateral Agent
(as the same may be amended or modified from time to time, the "Exchange
Agreement") shall be subject to the terms of this Subordination Agreement, and
(b) the Collateral Agent shall not knowingly take, and the Creditors shall not
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 Subordination Agreement
solely in its capacity as Collateral Agent under the Exchange Agreement, and not
otherwise. The Collateral Agent shall have no any liability or responsibility
for the actions or omissions of any Creditor, or for any Creditor's compliance
with (or failure to comply with) the terms of this Subordination Agreement. The
Collateral Agent shall not have individual liability to the Bank if it shall
mistakenly pay over or distribute to any Creditor (or the Borrower) any amounts
to which the Bank is entitled under this Subordination Agreement, so long as the
Collateral Agent is acting in good faith. Nothing in this Subordination
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 Subordination Agreement, and in performing or
observing any of the terms of this Subordination Agreement, and otherwise in
respect of any matter arising under or in respect of this Subordination
Agreement, the Collateral Agent shall enjoy and shall be protected by each of
the rights, immunities, indemnities and other protections set forth in the
Exchange Agreement; and any obligations, duties or liabilities to which the
Collateral Agent may be or become subject under or in respect of this
Subordination Agreement shall be subject to and limited by the terms of the
Exchange Agreement (including, without limitation, the terms of Section 11
thereof). Subject to the other provisions of this Section 17, 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 Exchange Agreement. The
Collateral Agent has no responsibility for the terms of this Subordination
Agreement or its sufficiency for any purpose.

     (iv) The Parties agree that the Fiscal Agent shall be responsible hereunder
solely for receiving and transmitting notices pursuant to Section 5(i) and (ii),
and shall have no responsibility for the performance by the Borrower or the
Creditors of their respective obligations hereunder. The Fiscal Agent is acting
hereunder as Fiscal Agent pursuant to A Fiscal Agency Agreement dated as of
January __ , 2002, among the Borrower and the Fiscal Agent, (the "Fiscal Agency
Agreement"), and not in its individual capacity. The Fiscal Agent shall not
knowingly take, and neither the Borrower nor the Creditors shall instruct or
direct the Fiscal Agent to take, any action that would be in violation of the
terms hereof.

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

                                       -4-
<Page>

     (vi) In entering into this Subordination Agreement, and in performing or
observing any of the terms of this Subordination Agreement, and otherwise in
respect of any matter arising under or in respect of this Subordination
Agreement, the Fiscal Agent shall enjoy and shall be protected by each of the
rights, immunities, indemnities and other protections set forth in the Fiscal
Agency Agreement; and any obligations, duties or liabilities to which the Fiscal
Agent may be or become subject under or in respect of this Subordination
Agreement shall be subject to and limited by the terms of the Fiscal Agency
Agreement. Subject to the other provisions of this Section 17, in no event shall
the Fiscal Agent have any liability hereunder that it would not have, nor shall
the Fiscal Agent be obligated to take any action hereunder that it would not be
required to take, under the terms of the Fiscal Agency Agreement. The Fiscal
Agent has no responsibility for the terms of this Subordination Agreement or its
sufficiency for any purpose.

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

                                 "Bank"

                                 SILICON VALLEY BANK


                                 By: /s/ John Peck
                                    ---------------------------

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

     Agreed to solely for purposes of Section 17 above:

     U. S. BANK NATIONAL ASSOCIATION,
     as Collateral Agent and as Fiscal Agent

     By: /s/ John A. Brennan
        --------------------------

     Title: Trust Officer
           -----------------------

                                       -5-
<Page>


                                        RHAPSODY FUND, LP

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS GENERAL PARTNER

                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        ARPEGGIO FUND

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS INVESTMENT ADVISOR


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        INTERNATIONAL MONETARY FUND
                                        -CONVERTIBLE ARBITRAGE ACCOUNT

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS INVESTMENT ADVISOR


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        CSV LIMITED

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS INVESTMENT ADVISOR


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

<Page>

                                        CITISAM, LTD.

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS INVESTMENT ADVISOR


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        ANDANTE FUND, LP

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS GENERAL PARTNER


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        VIVACE FUND, LP

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS GENERAL PARTNER


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

                                        ADAGIO FUND

                                        BY SYMPHONY ASSET MANAGEMENT LLC,
                                        AS INVESTMENT ADVISOR


                                        By: /s/ Neil Rudolph
                                           -----------------------------
                                           Name: Neil Rudolph
                                           Title: Chief Operating Officer

<Page>

     The undersigned approves of the terms of this Agreement.

     "Borrower"

     IBASIS, INC.


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

     Title: President and CEO
           -----------------------


     IBASIS GLOBAL, INC.


     By: /s/ Richard G. Tennant
        --------------------------

     Title: Treasurer and CEO
           -----------------------


     IBASIS SECURITIES CORPORATION.


     By: /s/ Gordon VanderBrug
        --------------------------

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

                                       -7-