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                                                                   EXHIBIT 10.42

                               AMENDMENT NO. 1 TO
                          SECURITIES EXCHANGE AGREEMENT

     This AMENDMENT NO. 1 TO SECURITIES EXCHANGE AGREEMENT (this "AMENDMENT")
dated as of February 21, 2002, is by and among iBasis, Inc., a Delaware
corporation (the "COMPANY"), iBasis Global, Inc., a Delaware corporation
("iBASIS GLOBAL", and together with the Company, the "BORROWER"), iBasis
Securities corporation, a Massachusetts corporation (the "GUARANTOR"), the
Symphony Funds identified on the signature pages hereto (the "SYMPHONY FUNDS")
and U.S. Bank National Association as Collateral Agent for the Holders (with its
successors and assigns, the "COLLATERAL AGENT").

     WHEREAS, the Borrowers, the Guarantor, the Symphony Funds and the
Collateral Agent are parties to a Securities Exchange Agreement dated as of
January 30, 2003 (as amended and in effect from time to time, the "SYMPHONY
EXCHANGE AGREEMENT"), pursuant to which the Symphony Funds exchanged an
aggregate principal amount of $30,200,000 of the Company's 5 3/4% Convertible
Subordinated Notes due 2005 for (a) an aggregate principal amount of $15,100,000
of the Borrower's 11.5% Senior Secured Notes due 2005 and (b) warrants
exercisable for an aggregate of 3,071,184 shares of Common Stock, $0.001 par
value, of the Company;

     WHEREAS, the Borrowers, the Guarantor and the Symphony Funds have agreed,
and the Collateral Agent has consented, on the terms and conditions set forth
herein, to amend certain provisions of the Symphony Exchange Agreement; and

     WHEREAS, capitalized terms which are used herein without definition and
which are defined in the Symphony Exchange Agreement shall have the same
meanings herein as in the Symphony Exchange Agreement.

     NOW, THEREFORE, in consideration of the foregoing premises and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrowers, the Guarantor, the Symphony Funds and the
Collateral Agent hereby agree as follows:

     Section 1.   AMENDMENT TO THE RECITALS TO THE SYMPHONY EXCHANGE AGREEMENT.
The Recitals to the Symphony Exchange Agreement are hereby amended by deleting
the words "(the "NOTES")" in clause (a) therein.

     Section 2.   AMENDMENT TO SECTION 1 OF THE SYMPHONY EXCHANGE AGREEMENT.
Section 1 of the Symphony Exchange Agreement is hereby amended by deleting the
definitions of "Fiscal Agency Agreement", "Notes" and "Warrant Agreement" in
their entirety and inserting the following new definitions in proper
alphabetical order in lieu thereof:

                  "FISCAL AGENCY AGREEMENT" means that Fiscal Agency Agreement,
     dated as of the date hereof, between the Company and the Fiscal Agent, as
     the same may be amended, modified or supplemented from time to time in
     accordance with the terms thereof.

                  "NOTES" means up to $28,750,000 aggregate principal amount of
     the Borrower's 11.5% Senior Secured Notes due 2005, issued pursuant to this
     Agreement or pursuant to a Permitted Exchange in which such Notes are
     issued without violating Section 8.4 herein.

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                  "WARRANT AGREEMENT" means the Amended and Restated Warrant and
     Registration Rights Agreement dated as of February 21, 2003, by the Company
     and U.S. Bank National Association, as Warrant Agent (as amended, modified
     or supplemented from time to time).

     Section 3.   AMENDMENT TO SECTION 13 OF THE SYMPHONY EXCHANGE AGREEMENT.
Section 13 of the Symphony Exchange Agreement is hereby amended by:

                  (a)   inserting the following text immediately after the words
     "Required Holders" and before the semi-colon in the fourth line of Section
     13.4:

                        ", and no such change, waiver, discharge or termination
                  shall be effective against the Collateral Agent unless and
                  until an executed copy thereof has been provided to the
                  Collateral Agent (and, in the case of any other Document,
                  subject to any other requirements applicable to such
                  amendment, change, waiver, discharge or termination set forth
                  in such Document)";

                  (b)   inserting the following new proviso at the end of the
     first sentence of Section 13.4:

                        "PROVIDED, FURTHER, HOWEVER, that no such change,
                  waiver, discharge or termination that alters the rights,
                  immunities or duties of the Collateral Agent shall take effect
                  without the Collateral Agent's express written consent;" and

                  (c)   inserting the following new sentence at the end of
     Section 13.4 therein:

                        "Notwithstanding anything to the contrary in this
                  Agreement, all Holders shall be deemed to be third-party
                  beneficiaries of all of the provisions of this Agreement that
                  relate to Holders, including but not limited to any provisions
                  that may only be waived or consented to by the "Required
                  Holders", or that may be initiated only by the "Demand
                  Holders", with such groups being determined for all purposes
                  of this Agreement with regard to all Holders, whether issued
                  pursuant to this Agreement or other exchanges in which such
                  Notes are issued without violating Section 8.3 or Section 8.4
                  hereof."

     Section 4.   CONSENT TO AMENDED AND RESTATED WARRANT AGREEMENT. Each of the
Symphony Funds hereby consents to the terms and conditions of, and the execution
and delivery by the Company and the Warrant Agent of, that certain Amended and
Restated Warrant and Registration Rights Agreement dated as of February 21,
2003, by the Company and U.S. Bank National Association, as Warrant Agent.

     Section 5    REPRESENTATIONS AND WARRANTIES. Each of the Borrowers, the
Guarantor, each Symphony Fund and the Collateral Agent, in each case solely with
respect to itself and on its own behalf, hereby represents and warrants to the
other parties as follows:

                  5.1   REPRESENTATION AND WARRANTIES IN THE SYMPHONY EXCHANGE
     AGREEMENT. The representations and warranties that it makes, if any, in the
     Symphony Exchange Agreement were true and correct in all material respects
     as of the date when made and continue to be true and correct in all
     material respects on the date hereof.

                  5.2   RATIFICATION, ETC. Except as expressly amended hereby,
     the Symphony Exchange Agreement is hereby ratified and confirmed in all
     respects and shall continue in full force and effect. The Symphony Exchange
     Agreement shall, together with this

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     Amendment, be read and construed as a single agreement. All references in
     the Symphony Exchange Agreement or any related agreement or instrument
     shall hereafter refer to the Symphony Exchange Agreement as amended hereby.

                  5.3   AUTHORITY, ETC. Its execution and delivery of this
     Amendment and its performance of its agreements and obligations under the
     Symphony Exchange Agreement, as amended hereby, are within such party's
     corporate authority and have been duly authorized by all necessary
     corporate action on the part of such party.

                  5.4   ENFORCEABILITY. This Amendment and the Symphony Exchange
     Agreement, as amended hereby, constitute the legal, valid and binding
     obligations of such party enforceable against such party in accordance with
     their terms.

     Section 6.   NO OTHER AMENDMENTS. Except as expressly provided in this
Amendment, all of the terms and conditions of the Symphony Exchange Agreement
remain in full force and effect.

     Section 7.   EXECUTION IN COUNTERPARTS. This Amendment may be executed in
any number of counterparts, but all such counterparts shall together constitute
but one instrument. In making proof of this Amendment it shall not be necessary
to produce or account for more than one counterpart signed by each party hereto
by and against which enforcement hereof is sought.

     Section 8.   MISCELLANEOUS. THIS AMENDMENT SHALL FOR ALL PURPOSES BE
CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE COMMONWEALTH OF
MASSACHUSETTS, WITHOUT REGARD TO THE PRINCIPLES OF CONFLICTS OF LAWS). The
captions in this Amendment are for convenience of reference only and shall not
define or limit the provisions hereof.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

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                                       -4-

     IN WITNESS WHEREOF, the undersigned have duly executed this Amendment as of
the date first set forth above.

                                 THE BORROWERS:

                                 iBASIS, INC.

                                 By:       /s/ Ofer Gneezy
                                    --------------------------------------------
                                    Name:      Ofer Gneezy
                                    Title: President and Chief
                                           Executive Officer

                                 iBASIS GLOBAL, INC.

                                 By:       /s/ Richard Tennant
                                    --------------------------------------------
                                    Name:      Richard Tennant
                                    Title: Treasurer and Chief Financial Officer

                                 THE GUARANTOR:

                                 iBASIS SECURITIES CORPORATION

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

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                                       -5-

                                 THE SYMPHONY FUNDS:

                                 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

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                                       -6-

                                 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

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                                       -7-

                                 THE COLLATERAL AGENT:

                                 U.S. BANK NATIONAL ASSOCIATION

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

                                                                   EXHIBIT 10.43

                               AMENDMENT NO. 1 TO
                             FISCAL AGENCY AGREEMENT

     This AMENDMENT NO. 1 TO FISCAL AGENCY AGREEMENT (this "AMENDMENT") dated as
of February 21, 2002, is by and among iBASIS, INC., a Delaware corporation
(together with its permitted successors and assigns, the "COMPANY"), iBASIS
GLOBAL, INC., a Delaware corporation (together with its permitted successors and
assigns, "iBASIS GLOBAL", and collectively with the Company, the "ISSUER"), and
U.S. BANK NATIONAL ASSOCIATION, as the fiscal agent, paying agent, note
registrar and authenticating agent (in such capacity, together with its
permitted successors and assigns, the "FISCAL AGENT").

     WHEREAS, the Issuer and the Fiscal Agent are parties to a Fiscal Agency
Agreement dated as of January 30, 2003 (as amended and in effect from time to
time, the "FISCAL AGENCY AGREEMENT"), pursuant to which the Issuer appointed the
Fiscal Agent to act as paying agent, registrar and transfer agent in respect of
the Issuer's 11.5% Senior Secured Notes due 2005 (the "NOTES");

     WHEREAS, the Issuer and the Fiscal Agent have agreed, on the terms and
conditions set forth herein, to amend certain provisions of the Fiscal Agency
Agreement to increase the principal amount of the Notes that may be issued
thereunder in accordance with Section 17(a)(vii) thereof; and

     WHEREAS, capitalized terms which are used herein without definition and
which are defined in the Fiscal Agency Agreement shall have the same meanings
herein as in the Fiscal Agency Agreement.

     NOW, THEREFORE, in consideration of the foregoing premises and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Issuer and the Fiscal Agent hereby agree as follows:

     Section 1. AMENDMENT TO SECTION 3(a) OF THE FISCAL AGENCY AGREEMENT.
Section 3(a) of the Fiscal Agency Agreement is hereby amended to substitute
"U.S. $28,750,000" for "U.S. $15,100,000."

     Section 2. AMENDMENT TO SECTION 17(a)(vii) OF THE FISCAL AGENCY AGREEMENT.
Section 17(a)(vii) of the Fiscal Agency Agreement is hereby deleted in its
entirety.

     Section 3. NO OTHER AMENDMENTS. Except as expressly provided in this
Amendment, all of the terms and conditions of the Fiscal Agency Agreement remain
in full force and effect.

     Section 4. EXECUTION IN COUNTERPARTS. This Amendment may be executed in any
number of counterparts, but all such counterparts shall together constitute but
one instrument. In making proof of this Amendment it shall not be necessary to
produce or account for more than one counterpart signed by each party hereto by
and against which enforcement hereof is sought.

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     Section 5. MISCELLANEOUS. THIS AMENDMENT SHALL FOR ALL PURPOSES BE
CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE COMMONWEALTH OF
MASSACHUSETTS (EXCLUDING THE LAWS APPLICABLE TO CONFLICTS OR CHOICE OF LAW). The
captions in this Amendment are for convenience of reference only and shall not
define or limit the provisions hereof.

                  [Remainder of Page Intentionally Left Blank]

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                                       -2-

     IN WITNESS WHEREOF, the undersigned have duly executed this Amendment as of
the date first set forth above.

                                              THE ISSUER:

                                              iBASIS, INC.

                                              By:      /s/ Ofer Gneezy
                                                 -------------------------------
                                                 Name: Ofer Gneezy
                                                 Title: President and Chief
                                                 Executive Officer

                                              iBASIS GLOBAL, INC.

                                              By:      /s/ Richard Tennant
                                                 -------------------------------
                                                 Name: Richard Tennant
                                                 Title: Treasurer and Chief
                                                        Financial Officer

                                              THE FISCAL AGENT:

                                              U.S. BANK NATIONAL ASSOCIATION

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

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