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                                                                    Exhibit 31.1

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
                      AS ADOPTED PURSUANT TO SECTION 302 OF
                         THE SARBANES-OXLEY ACT OF 2002

                              ANNUAL CERTIFICATION
            PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

         I, Ofer Gneezy, President and CEO of iBasis, Inc., a Delaware
corporation, doing business in Burlington, Massachusetts, certify that:

                  1. I have reviewed this annual report of Form 10-K of iBasis,
         Inc.;

         2. Based on my knowledge, this annual report does not contain any
untrue statement of a material fact or omit to state a material fact necessary
to make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by this
annual report;

         3. Based on my knowledge, the financial statements, and other financial
information included in this annual report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
registrant as of, and for, the periods presented in this annual report;

         4. The registrant's other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in
Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and we have:

         a) designed such disclosure controls and procedures to ensure that
            material information relating to the registrant, including its
            consolidated subsidiaries, is made known to us by others within
            those entities, particularly during the period in which this annual
            report is being prepared;

         b) (Intentionally left blank)

         c) Evaluated the effectiveness of the registrant's disclosure controls
            and procedures and presented in this report our conclusions about
            the effectiveness of the disclosure controls and procedures, as of
            the end of the period covered by this report based on such
            evaluation; and

         d) Disclosed in this report any change in the registrant's internal
            control over financial reporting that occurred during the
            registrant's most recent fiscal quarter (the registrant's fourth
            fiscal quarter in the case of an annual report) that has
            materially affected, or is reasonably likely to materially affect,
            the registrant's internal control over financial reporting; and

         5. The registrant's other certifying officers and I have disclosed,
based on our most recent evaluation to the registrant's auditors and the audit
committee of registrant's board of directors (or persons performing the
equivalent functions):

         a) all significant deficiencies in the design or operation of internal
            controls which could adversely affect the registrant's ability to
            record, process, summarize and report financial data and have
            identified for the registrant's auditors any material weaknesses in
            internal controls; and

         b) any fraud, whether or not material, that involves management or
            other employees who have a significant role in the registrant's
            internal controls; and

         6. The registrant's other certifying officers and I have indicated in
this annual report whether or not there were significant changes in internal
controls or in other factors that could significantly affect internal controls
subsequent to the date of our most recent evaluation, including any corrective
actions with regard to significant deficiencies and material weaknesses.

                                                /s/Ofer Gneezy
                                                Chief Executive Officer
                 February 27, 2004              (Principal Executive Officer)