Exhibit 31.2

CERTIFICATION

I, Charles S. Wiesenhart Jr., certify that:

1. I have reviewed this quarterly report on Form 10-Q of FiberNet Telecom Group, Inc.;

2. Based on my knowledge, this quarterly 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 quarterly report;

3. Based on my knowledge, the condensed
consolidated interim financial statements, and other financial information included in this quarterly 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 quarterly report;

4. The registrants other certifying officer 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 Rule 13a-15(f) and 15(d)-15(f)) for the registrant and we 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 quarterly 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 quarterly 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 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 and I have disclosed, based on our most recent evaluation
of internal control over financial reporting, to the registrants registered public accounting firm 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:
October 30, 2008



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|/s/ Charles S. Wiesenhart Jr.                                                   
|Charles S. Wiesenhart Jr.                                                       
|Vice PresidentFinance and Chief Financial Officer (Principal Financial Officer)