Exhibit 31.2  CERTIFICATION UNDER SECTION 302 OF
THE SARBANES-OXLEY ACT OF 2002  I, Richard Tennant, certify that:  1.  I have reviewed this Annual Report on Form 10-K
of iBasis, Inc.;  2.  Based on my knowledge, this 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 report;  3.  Based on my knowledge, the financial
statements, and other financial information included in this 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 report;  4.  The registrants other certifying officer(s) 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))
and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and
15d-15(f) for the registrant and have:  a)  designed such disclosure controls and
procedures, or caused such disclosure controls and procedures to be designed
under our supervision, 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
report is being prepared;  b)  designed such internal control over financial
reporting, or caused such internal control over financial reporting to be
designed under our supervision, to provide reasonable assurance regarding the
reliability of financial reporting and the preparation of financial statements
for external purposes in accordance with generally accepted accounting
principles;  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 officer(s) and
I have disclosed, based on our most recent evaluation of internal control over
financial reporting, to the registrants auditors and the audit committee of
the registrants board of directors (or persons performing the equivalent
functions):  a)  all significant deficiencies and material
weaknesses in the design or operation of internal control over financial
reporting which are reasonably likely to adversely affect the registrants
ability to record, process, summarize and report financial information; and  b)  any fraud, whether or not material, that
involves management or other employees who have a significant role in the
registrants internal control over financial reporting.  Date: March 13, 2009
  /s/ Richard TennantRichard TennantSenior Vice President and Chief Financial Officer(Principal Financial and Accounting Officer)