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                                                                    EXHIBIT 32.2

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES/OXLEY ACT OF 2002

     In connection with the Annual Report of iBasis, Inc. (the "Company") on
Form 10-K for the year ended December 31, 2003 as filed with the Securities and
Exchange Commission (the "Report"), I, Richard Tennant, Chief Financial Officer
of the Company, certify, pursuant to Section 1350 of Chapter 63 of Title 18,
United States Code, that this Report fully complies with the requirements of
Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that the
information contained in this Report fairly presents, in all material respects,
the financial condition and results of operations of the Company.


Date: February 27, 2004                  By:  /s/Richard Tennant
                                              ---------------------------------
                                              Richard Tennant
                                              Chief Financial Officer
                                              and Principal Accounting Officer