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Exhibit 31.2

CERTIFICATIONS

I, Wayne M. Rehberger, certify that:

1. I have reviewed this annual report on
Form 10-K of XO Communications, Inc.;

2. Based on my knowledge, this annual report
does not contain any untrue statement of a material fact or omit
to state a material fact necessary to make 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
annual 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 annual
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)) for the registrant and have:



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| | 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 annual
    report is being prepared;
|
| | b) | evaluated the effectiveness of the
    registrants disclosure controls and procedures and
    presented in this annual 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                                                                                               
|
| | c) | 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 auditors and the audit committee of
registrants board of directors (or persons performing the
equivalent function):



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| | 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 controls over financial reporting.                                                                                                      

Date: March 15, 2004

| |                                   
| | ----------------------------------
| | /s/ WAYNE M. REHBERGER            
| |                                   
| | Wayne M. Rehberger                
| | Executive Vice President and Chief
| | Financial Officer                 
|
| | (Principal Financial Officer)