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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 Quarterly Report of iBasis, Inc. (the "Company") on Form 10-Q for the year ended December 31, 2004 as filed with the Securities and Exchange Commission (the "Report"), I, Richard Tennant, of iBasis, 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: March 25, 2005 /s/  RICHARD TENNANT Richard Tennant
Chief Financial Officer
and Principal Accounting Officer

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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