VOTING AGREEMENT

VOTING AGREEMENT, dated as of May 4, 2006 (this ?Agreement?), among U.S. TelePacific Holdings Corp., a Delaware corporation (?Parent?) and the stockholders of Mpower Holding Corporation, a Delaware corporation (the ?Company?) listed on Schedule A hereto (each a ?Stockholder? and collectively the ?Stockholders?).

WHEREAS, concurrently herewith, Parent, TPMC Acquisition Corp., a Delaware corporation and wholly-owned subsidiary of Parent (?Merger Sub?), and the Company are entering into an Agreement and Plan of Merger (the ?Merger Agreement?) pursuant to which (and subject to the terms and conditions set forth therein) Merge Sub will merge with and into the Company, with the Company continuing as the surviving corporation in the merger (the ?Merger?);

WHEREAS, the Stockholders are the record and beneficial owners of the shares of common stock, par value $0.001 per share, of the Company (the ?Company Common Stock?) as set forth on Schedule A hereto (collectively, the ?Owned Shares?; the Owned Shares, including any shares of the Company Common Stock acquired by any Stockholder after the date hereof and prior to the termination hereof, including without limitation, as a result of a stock dividend, stock split, recapitalization, combination, reclassification, exchange, or change of such shares, or upon exercise or conversion of any securities, that are, from time to time, owned of record or beneficially by any Stockholder, are collectively referred to herein as the ?Covered Shares?);

WHEREAS, in order to induce Parent and Merger Sub to enter into the Merger Agreement and to proceed with the transactions contemplated thereby, including the Merger, Parent and the Stockholders are entering into this Agreement; and

WHEREAS, the Stockholders acknowledge that Parent and Merger Sub are entering into the Merger Agreement in reliance on the representations, warranties, covenants and other agreements of the Stockholders set forth in this Agreement and would not enter into the Merger Agreement if any Stockholder did not enter into this Agreement.

NOW, THEREFORE, in consideration of the foregoing and the mutual covenants and agreements herein contained, and intending to be legally bound hereby, Parent and the Stockholders hereby agree as follows:

1.             Agreement to Vote. Capitalized terms used but not defined in this Agreement shall have the meanings ascribed to them in the Merger Agreement. Prior to the Termination Date (as defined herein), each Stockholder irrevocably and unconditionally agrees that it shall at any meeting of the stockholders of the Company (whether annual or special and whether or not an adjourned or postponed meeting), however called, or in connection with any written consent of stockholders of the Company (i) when a meeting is held, appear at such meeting or otherwise cause the Covered Shares to be counted as present thereat for the purpose of establishing a quorum, and respond to each request by the Company for written consent, if any, and (ii) vote (or consent), or cause to be voted at such meeting (or validly execute and return and cause such consent to be granted with respect to), all Covered Shares (A) in favor of the Merger and any