QuickLinks -- Click here to rapidly navigate through this document
CERTIFICATIONS UNDER SECTION 906
OF THE SARBANES-OXLEY ACT OF 2002
Pursuant to section 906 of the Sarbanes-Oxley Act of 2002 (subsections (a) and (b) of section 1350, chapter 63 of title 18, United States Code), each of the undersigned officers of iBasis, Inc., a Delaware corporation (the "Company"), does hereby certify, to such officer's knowledge, that:
The Quarterly Report on Form 10-Q for the three months ended September 30, 2009 (the "Form 10-Q") of the Company fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and the information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Company.
| Date: November 9, 2009 | /s/ OFER GNEEZY Ofer Gneezy President and Chief Executive Officer (Principal Executive Officer) | |
Date: November 9, 2009 | /s/ RICHARD TENNANT Richard Tennant Senior Vice President and Chief Financial Officer (Principal Financial and Accounting Officer) |