Exhibit 4.4

JOINDER AGREEMENT

December 6, 2010

Pursuant to Section 3(j) of the Purchase Agreement, such section being an inducement to the Representatives (on behalf of the Initial Purchasers) referred to below to execute the Purchase Agreement, the undersigned hereby execute this joinder agreement (this “Joinder Agreement”), whereby each of the undersigned agrees, on a joint and several basis, to accede to the terms of the Registration Rights Agreement (the “Registration Rights Agreement”), dated as of December 2, 2010 (the “Issue Date”), between PAETEC Escrow Corporation (the “Escrow Issuer”), a Delaware corporation and a wholly-owned subsidiary of PAETEC Holding Corp. (the “Parent”), and Deutsche Bank Securities Inc. (“DB”), Merrill Lynch, Pierce, Fenner & Smith Incorporated (“ML” and, together with DB, the “Representatives”), Goldman Sachs & Co. (“GS”) and Morgan Stanley & Co. Incorporated (“MS” and, together with the Representatives and GS, the “Initial Purchasers”). Capitalized terms used in this Joinder Agreement without definition have the respective meanings given to them in the Registration Rights Agreement.

The Parent hereby undertakes to perform all of the obligations of the Company set forth therein, as though the Parent had entered into the Registration Rights Agreement on the Issue Date. Each of the undersigned PAETEC Guarantors and Cavalier Entities undertakes to perform, on a joint and several basis, all of the obligations of the Note Guarantors set forth therein, as though the undersigned PAETEC Guarantors and Cavalier Entities had entered into the Registration Rights Agreement on the Issue Date. Each of the undersigned agrees that such obligations include, without limitation, (a) the Parent’s assumption of all of the obligations of the Company to perform and comply with all of the agreements thereof contained in the Registration Rights Agreement, (b) the PAETEC Guarantors’ and Cavalier Entities’ assumption of all of the obligations of the Note Guarantors to perform and comply with all of the agreements thereof contained in the Registration Rights Agreement and (c) the Parent’s, the PAETEC Guarantors’ and the Cavalier Entities’ assumption, to the same extent as set forth therein but on a joint and several basis, of all of the Company’s and the Note Guarantors’ indemnification and other obligations contained in Section 8 of the Registration Rights Agreement.

This Joinder Agreement shall be governed by and construed in accordance with the laws of the State of New York applicable to agreements made and to be performed in New York State.

This Joinder Agreement may be executed in any number of counterparts and by the parties hereto in separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement. Delivery of an executed counterpart of a signature page by facsimile, e-mail or other electronic means shall be effective as delivery of a manually executed counterpart.

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IN WITNESS WHEREOF, the parties hereto have executed this Joinder Agreement as of the date first written above.