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                                                                     EXHIBIT 4.2

     UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY (55 WATER STREET, NEW YORK, NEW YORK) (THE
"DEPOSITARY", WHICH TERM INCLUDES ANY SUCCESSOR DEPOSITARY FOR THE CERTIFICATES)
TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT,
AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH
OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY (AND
ANY PAYMENT HEREIN IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED
BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY), ANY TRANSFER, PLEDGE, OR
OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH
AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

     THE NOTE EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE UNITED STATES
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND ACCORDINGLY MAY
NOT BE OFFERED OR SOLD EXCEPT AS SET FORTH BELOW. BY ITS ACQUISITION HEREOF, THE
HOLDER (1) REPRESENTS THAT IT IS (A) A "QUALIFIED INSTITUTIONAL BUYER" (AS
DEFINED IN RULE 144A UNDER THE SECURITIES ACT), (2) AGREES THAT IT WILL NOT
WITHIN TWO YEARS AFTER THE ORIGINAL ISSUANCE OF THIS NOTE RESELL OR OTHERWISE
TRANSFER THIS NOTE EXCEPT (A) TO iBASIS, INC. OR ANY SUBSIDIARY THEREOF, (B) TO
A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE
SECURITIES ACT, OR (C) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN
DECLARED EFFECTIVE UNDER THE SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE
AT THE TIME OF SUCH TRANSFER); (3) PRIOR TO SUCH TRANSFER (OTHER THAN A TRANSFER
PURSUANT TO CLAUSE (2)(C) ABOVE), IT WILL FURNISH TO U.S. NATIONAL BANK
ASSOCIATION, AS FISCAL AGENT (OR A SUCCESSOR FISCAL AGENT, AS APPLICABLE), SUCH
CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS THE FISCAL AGENT MAY
REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
REQUIREMENTS OF THE SECURITIES ACT; AND (4) AGREES THAT IT WILL DELIVER TO EACH
PERSON TO WHOM THIS NOTE IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF
THIS LEGEND. IN CONNECTION WITH ANY TRANSFER OF THIS NOTE, THE HOLDER MUST CHECK
THE APPROPRIATE BOX SET FORTH ON THE REVERSE HEREOF RELATING TO THE MANNER OF
SUCH TRANSFER AND SUBMIT THIS CERTIFICATE TO U.S. NATIONAL BANK ASSOCIATION, AS
FISCAL AGENT (OR A SUCCESSOR FISCAL AGENT, AS APPLICABLE). THE FISCAL AGENCY
AGREEMENT CONTAINS A PROVISION REQUIRING THE FISCAL AGENT TO REFUSE TO REGISTER
ANY TRANSFER OF THIS NOTE IN VIOLATION OF THE FOREGIONG RESTRICTION.

     THE TERMS OF THIS NOTE ARE SUBJECT TO THAT CERTAIN SUBORDINATION AGREEMENT
DATED AS OF JANUARY 30, 2003, AMONG SILICON VALLEY BANK, THE

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CREDITORS NAMED THEREIN AND U.S. BANK NATIONAL ASSOCIATION, AS COLLATERAL AGENT
AND FISCAL AGENT

<Page>

                                  iBASIS, INC.

                               iBASIS GLOBAL, INC.

                       11.5% SENIOR SECURED NOTE DUE 2005

                                                              CUSIP: 450732 AB 8

No.: N-1                                                             $15,100,000

     iBasis, Inc., a corporation duly organized and validly existing under the
laws of the State of Delaware, and iBasis Global, Inc., a corporation duly
organized and validly existing under the laws of the State of Delaware (herein
collectively called the "Issuer", which term includes any successor corporation
under the Fiscal Agency Agreement referred to on the reverse hereof), for value
received hereby, on a joint and several basis, promise to pay to Cede & Co. or
registered assigns, the principal sum of Fifteen Million One Hundred Thousand
Dollars ($15,100,000) on January 15, 2005, at the office or agency of the Issuer
maintained for that purpose in accordance with the terms of the Fiscal Agency
Agreement, in such coin or currency of the United States of America as at the
time of payment shall be legal tender for the payment of public and private
debts, and to pay interest, semi-annually on January 15 and July 15 of each
year, commencing July 15, 2003, on said principal sum at said office or agency,
in like coin or currency, at the rate per annum of 11.5%, from January 15 or
July 15, as the case may be, next preceding the date of this Note to which
interest has been paid or duly provided for, unless the date hereof is a date to
which interest has been paid or duly provided for, in which case from the date
of this Note, or unless no interest has been paid or duly provided for on the
Notes, in which case from January 30, 2003, until payment of said principal sum
has been made or duly provided for. Notwithstanding the foregoing, if the date
hereof is after any January 1 or July 1, as the case may be, and before the
following January 15 or July 15, this Note shall bear interest from such January
15 or July 15; provided, however, that if the Issuer shall default in the
payment of interest due on such January 15 or July 15, then this Note shall bear
interest from the next preceding January 15 or July 15 to which interest has
been paid or duly provided for or, if no interest has been paid or duly provided
for on such Note, from January 30, 2003. Except as otherwise provided in the
Fiscal Agency Agreement or the Exchange Agreement referred to on the reverse
hereof, the interest payable on the Note pursuant to the Exchange Agreement on
any January 15 or July 15 will be paid to the Person entitled thereto as it
appears in the Note register at the close of business on the record date, which
shall be the January 1 or July 1 (whether or not a Business Day) next preceding
such January 15 or July 15, as provided in the Fiscal Agency Agreement;
provided, however, that any such interest not punctually paid or duly provided
for shall be payable as provided in the Exchange Agreement or the Fiscal Agency
Agreement. Interest may, at the option of the Issuer, be paid either (i) by
check mailed to the registered address of such Person (provided that the holder
of Notes with an aggregate principal amount in excess of $2,000,000 shall, at
the written election of such holder, be paid by wire transfer of immediately
available funds) or (ii) by transfer to an account maintained by such Person
located in the United States; provided, however, that payments to the Depositary
will be made by wire transfer of immediately available funds to the account of
the Depositary or its nominee.

     Reference is made to the further provisions of this Note set forth on the
reverse hereof, including, without limitation, provisions subordinating the
payment of principal of and premium, if

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any, and interest on the Notes to the prior payment in full of all Senior Debt,
as defined in the Subordination Agreement referred to on the reverse hereof.
Such further provisions shall for all purposes have the same effect as though
fully set forth at this place.

     This Note shall be deemed to be a contract made under the laws of The
Commonwealth of Massachusetts, and for all purposes shall be construed in
accordance with and governed by the laws of The Commonwealth of Massachusetts,
without regard to the principles of conflicts of laws.

     This Note shall not be valid or become obligatory for any purpose until the
certificate of authentication hereon shall have been manually signed by the
Fiscal Agent or a duly authorized authenticating agent under the Fiscal Agency
Agreement.

<Page>

     IN WITNESS WHEREOF, the Issuer has caused this Note to be duly executed.

                                        iBASIS, INC.


                                        By: /s/ Ofer Gneezy
                                           -----------------------------
                                           Name:  Ofer Gneezy
                                           Title: President and CEO


                                        iBASIS GLOBAL, INC.


                                        By: /s/ Richard G. Tennant
                                           -----------------------------
                                           Name:  Richard G. Tennant
                                           Title: Treasurer and CFO

Dated: January 30, 2003

FISCAL AGENT'S CERTIFICATE OF AUTHENTICATION

This is one of the Notes described in the within-named Fiscal Agency Agreement.

U.S. BANK NATIONAL ASSOCIATION, as Fiscal Agent


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

By:
    ------------------------------------
         As Authenticating Agent
      (if different from Fiscal Agent)

<Page>

                                 REVERSE OF NOTE

                                  iBASIS, INC.
                               iBASIS GLOBAL, INC.

                       11.5% SENIOR SECURED NOTES DUE 2005

     This Note is one of a duly authorized issue of Notes of the Issuer,
designated as its 11.5% Senior Secured Notes Due 2005 (herein called the
"Notes"), limited to the aggregate principal amount of $15,100,000, all issued
or to be issued under and pursuant to a Securities Exchange Agreement dated as
of January 30, 2003 (herein called the "Exchange Agreement"), among the Issuer,
iBasis Securities Corporation, the Symphony Funds party thereto and U.S. Bank
National Association, as collateral agent (herein called the "Collateral Agent")
to which Exchange Agreement and all exchange agreements supplemental thereto
reference is hereby made for a description of the rights, limitations of rights,
obligations, duties and immunities thereunder of the Collateral Agent, the
Issuer and the holders of the Notes. The Issuer has appointed U.S. Bank National
Association as fiscal agent, (herein called the "Fiscal Agent") and as paying
agent in respect of the Notes upon the terms and subject to the conditions
contained in a Fiscal Agency Agreement dated as of January 30, 2003 (herein
called the "Fiscal Agency Agreement"), between the Issuer and the Fiscal Agent.

     In case an Event of Default (as defined in the Exchange Agreement) shall
have occurred and be continuing, the principal of, premium, if any, and accrued
interest on all Notes may be declared by either the Collateral Agent or the
holders of not less than 25% in aggregate principal amount of the Notes then
outstanding, and upon said declaration shall become, due and payable, in the
manner, with the effect and subject to the conditions provided in the Exchange
Agreement.

     The Exchange Agreement contains provisions prohibiting the changing,
waiver, discharge or termination of the Exchange Agreement without the consent
of each holder of a Note directly affected thereby if such change, waiver,
discharge or termination shall (i) extend the fixed maturity of any Note, or
reduce the rate or extend the time of payment of interest thereon, or reduce the
principal amount thereof, (ii) amend, modify or waive the provisions of Section
13.4 of the Exchange Agreement, (iii) reduce the percentage specified in, or
otherwise modify the definition of "Demand Holders" or "Required Holders" stated
therein, (iv) consent to the assignment or transfer by the Issuer of any of its
rights and obligations under the Exchange Agreement, (v) establish any new
obligations for any holder of a Note not relating to the subject matter of the
Exchange Agreement or (ii) release all or substantially all of the collateral or
guarantees with respect to the Obligations specified in the Exchange Agreement.
Subject to the provisions of the Exchange Agreement, the holders of a majority
in aggregate principal amount of the Notes at the time outstanding may on behalf
of the holders of all of the Notes waive any past Default or Event of Default
under the Exchange Agreement and its consequences except a default in the
payment of interest. Any such consent or waiver by the holder of this Note
(unless revoked as provided in the Exchange Agreement) shall be conclusive and
binding upon such holder and upon all future holders and owners of this Note and
any Notes which may be issued in exchange or substitution hereof, irrespective
of whether or not any notation thereof is made upon this Note or such other
Notes.

<Page>

     The indebtedness evidenced by the Notes is, to the extent and in the manner
provided in the Subordination Agreement dated as of January 30, 2003 (herein
called the "Subordination Agreement"), among the Investors party thereto,
Silicon Valley Bank, and U.S. Bank National Association, subordinated and
subject in right of payment to the prior payment in full of all Senior Debt (as
defined in the Subordination Agreement), and this Note is issued subject to the
provisions of the Subordination Agreement with respect to such subordination.
Each holder of this Note, by accepting the same, agrees to and shall be bound by
such provisions.

     No reference herein to the Exchange Agreement, the Fiscal Agency Agreement
or the Subordination Agreement and no provision of this Note or of the Exchange
Agreement, the Fiscal Agency Agreement or the Subordination Agreement shall
alter or impair the obligation of the Issuer, which is absolute and
unconditional, to pay the principal of and any premium and interest on this Note
at the place, at the respective times, at the rate and in the coin or currency
herein prescribed.

     Interest on the Notes shall be computed on the basis of a 360-day year of
twelve 30-day months.

     The Notes are issuable in registered form, without coupons, in
denominations of $1,000 principal amount and any integral multiple of $1,000. At
the office or agency of the Issuer referred to on the face hereof, and in the
manner and subject to the limitations provided in the Exchange Agreement,
without payment of any service charge but with payment of a sum sufficient to
cover any tax, assessment or other governmental charge that may be imposed in
connection with any registration or exchange of Notes, Notes may be exchanged
for a like aggregate principal amount of Notes of any other authorized
denominations.

     The Notes may be prepaid at the election of the Issuer, as a whole or in
part from time to time, at any time, upon notice as set forth in Section 4.2 of
the Exchange Agreement, at the following prepayment prices (expressed in
percentages of the outstanding principal amount of the Note, as the case may be,
being prepaid) plus accrued and unpaid interest on such prepaid principal amount
to the prepayment date, MINUS the number of percentage points reflected by the
product of (i) 10.1695 and (ii) the difference between (A) the average closing
trading price of the Common Stock of iBasis, Inc. (the "Common Stock") for the
five trading days immediately prior to, but not including, the date of such
prepayment and (B) the Common Stock price denoted below in the column titled
"Minimum Common Stock Price" (the "Note Prepayment Price"); provided, however,
that in no event shall the Note Prepayment Price be less than 100% of the
outstanding principal amount of the Notes to be prepaid, plus accrued and unpaid
interest on such principal amount to the prepayment date:

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<Table>
<Caption>
--------------------------------------------------------------------------------------------
                                                      PERCENTAGE OF
                                                      OUTSTANDING PRINCIPAL   MINIMUM COMMON
DATE OF PREPAYMENT                                    AMOUNT                  STOCK PRICE
--------------------------------------------------------------------------------------------
         AFTER           PRIOR TO AND INCLUDING
--------------------------------------------------------------------------------------------
<S>                               <C>                             <C>                  <C>
November 15, 2002                 January 15, 2003                124.9167%            $2.00
--------------------------------------------------------------------------------------------
January 15, 2003                  July 15, 2003                   123.0000%            $2.25
--------------------------------------------------------------------------------------------
July 15, 2003                     January 15, 2004                117.2500%            $3.50
--------------------------------------------------------------------------------------------
January 15, 2004                  July 15, 2004                   111.5000%            $4.25
--------------------------------------------------------------------------------------------
July 15, 2004                     January 15, 2005                105.7500%            $5.00
--------------------------------------------------------------------------------------------
</Table>

     If a Change of Control (as defined in the Exchange Agreement) occurs at any
time prior to maturity of the Notes, the Issuer shall, within one Business Day,
make an offer to prepay all of the Notes then outstanding at the Note Prepayment
Price set forth above. If the Issuer or any Subsidiary receives any Net Asset
Sale Proceeds (as defined in the Exchange Agreement) in excess of $250,000 (or
if a Default or an Event of Default shall then exist, regardless of amount),
which in each such case does not result in a Change of Control, then the Issuer
shall, within one Business Day (or cause its Subsidiary receiving such proceeds
to pay) to the holders as a prepayment of the Notes the lesser of (a) the amount
of such Net Asset Sale Proceeds and (b) the Aggregate Prepayment Amount
(excluding any portion of such Net Asset Sale Proceeds which so long as no
Default or Event of Default exists, (x) in the case of proceeds of business
interruption insurance, is used in the ordinary course of the Issuer's and its
Subsidiaries' business and (y) in the case of proceeds of casualty insurance, is
applied for the purpose of replacing, repairing, restoring or rebuilding the
relevant tangible property).

     Upon due presentment for registration of transfer of this Note at the
office or agency of the Issuer maintained for that purpose in accordance with
the terms of the Fiscal Agency Agreement, a new Note or Notes of authorized
denominations for an equal aggregate principal amount will be issued to the
transferee in exchange thereof; subject to the limitations provided in the
Exchange Agreement and the Fiscal Agency Agreement, without charge except for
any tax, assessment or other governmental charge imposed in connection
therewith.

     The Issuer, the Fiscal Agent, any authenticating agent, any paying agent
and any Note registrar may deem and treat the registered holder hereof as the
absolute owner of this Note (whether or not this Note shall be overdue and
notwithstanding any notation of ownership or other writing hereon made by anyone
other than the Issuer or any Note registrar) for the purpose of receiving

<Page>

payment hereof, or on account hereof, for the conversion hereof and for all
other purposes, and neither the Issuer nor the Fiscal Agent nor any other
authenticating agent nor any paying agent nor other conversion agent nor any
Note registrar shall be affected by any notice to the contrary. All payments
made to or upon the order of such registered holder shall, to the extent of the
sum or sums paid, satisfy and discharge liability for monies payable on this
Note.

     No recourse for the payment of the principal of or any premium or interest
on this Note, or for any claim based hereon or otherwise in respect hereof, and
no recourse under or upon any obligation, covenant or agreement of the Issuer in
the Exchange Agreement or any supplemental exchange agreement or in any Note, or
because of the creation of any indebtedness represented thereby, shall be had
against any incorporator, stockholder, employee, agent, officer or director or
subsidiary, as such, past, present or future, of the Issuer or of any successor
corporation, either directly or through the Issuer or any successor corporation,
whether by virtue of any constitution, statute or rule of law or by the
enforcement of any assessment or penalty or otherwise, all such liability being,
by acceptance hereof and as part of the consideration for the issue hereof,
expressly waived and released.

     This Note shall be deemed to be a contract made under the laws of The
Commonwealth of Massachusetts, and for all purposes shall be construed in
accordance with the laws of The Commonwealth of Massachusetts, without regard to
principles of conflicts of laws.

     Terms used in this Note and defined in the Exchange Agreement are used
herein as therein defined.

<Page>

                                  ABBREVIATIONS

     The following abbreviations, when used in the inscription of the face of
this Note, shall be construed as though they were written out in full according
to applicable laws or regulations.

     TEN COM - as tenants in common

     TEN ENT - as tenant by the entireties

     JT TEN - as joint tenants with right of survivorship and not as tenants in
     common

     UNIF GIFT MIN ACT - ____________ Custodian _____________
                            (Cust)                (Minor)

     under Uniform Gifts to Minors Act

     --------------------------------------------
                          (State)

     Additional abbreviations may also be used though not in the above list.

<Page>

                                   ASSIGNMENT

     FOR VALUE RECEIVED the undersigned hereby sell(s), assign(s) and
transfer(s) unto

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

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

PLEASE INSERT SOCIAL SECURITY OR
OTHER IDENTIFYING NUMBER OF ASSIGNEE

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

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

-------------------------------------------------------------
           (Please print or typewrite name and address
             including postal zip code of assignee)

the within Note and all rights thereunder, and hereby irrevocably constitutes
and appoints

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

Attorney to transfer said Note on the books of the Issuer, with full power of
substitution in the premises.

     In connection with any transfer of the Note (other than any transfer
pursuant to a registration statement that has been declared effective under the
Securities Act), the undersigned confirms that such Note is being transferred:

<Page>

     / / To iBasis, Inc. or a subsidiary thereof; or

     / / Pursuant to and in compliance with Rule 144A under the Securities Act
         of 1933, as amended;

and unless the box below is checked, the undersigned confirms that such Note is
not being transferred to an "affiliate" of the Issuer as defined in Rule 144
under the Securities Act of 1933, as amended (an "Affiliate").

    / / The transferee is an Affiliate of the Issuer.

Dated:
      -------------------

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

                                        ----------------------------------------
                                        Signature(s)

                                        Signature(s) must be guaranteed by an
                                        "eligible guarantor institution" meeting
                                        the requirements of the Note registrar,
                                        which requirements include membership or
                                        participation in the Security Transfer
                                        Agent Medallion Program ("STAMP") or
                                        such other "signature guarantee program"
                                        as may be determined by the Note
                                        registrar in addition to, or in
                                        substitution for, STAMP, all in
                                        accordance with the Securities Exchange
                                        Act of 1934, as amended.

                                        ----------------------------------------
                                        Signature Guarantee

NOTICE: The signature of the assignment must correspond with the name as written
upon the face of the Note in every particular without alteration or enlargement
or any change whatever.