SUMMARY

This summary highlights selected information from this joint proxy statement/prospectus and may not contain all of the information that is important to you. To understand the agreement and plan of merger and the mergers fully and for a more complete description of the legal terms of the agreement and plan of merger and the mergers, you should carefully read this entire joint proxy statement/prospectus and the other documents to which we have referred you. See “Where You Can Find More Information” beginning on page 283. We have included page references parenthetically to direct you to a more complete description of the topics presented in this summary.

References to “we” or “our” and other first person references and to “PAETEC Holding” in this joint proxy statement/prospectus refer to PAETEC Holding Corp. and are intended, unless the context indicates otherwise, to refer to PAETEC Holding Corp. and its consolidated subsidiaries following completion of the mergers. PAETEC Holding was incorporated under the name WC Acquisition Holdings Corp. and its name will be changed to PAETEC Holding Corp. prior to the completion of mergers.

Except where indicated otherwise, as used in this joint proxy statement/prospectus:

US LEC has two classes of outstanding shares of capital stock, its Class A common stock, which we refer to as the “US LEC common stock,” and its Series A convertible preferred stock, which is convertible into the US LEC common stock and which we refer to as the “US LEC preferred stock.”

In this joint proxy statement/prospectus, we refer to:

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The effective time of the PAETEC merger and the effective time of the US LEC merger will occur simultaneously. We refer to the effective time of the two mergers as the “effective time of the mergers” or the “effective time.”

If the mergers are completed, PAETEC stockholders are currently expected to receive 1.623 shares of PAETEC Holding common stock for each share of PAETEC common stock held and US LEC stockholders are currently expected to receive 1.000 share of PAETEC Holding common stock for each share of US LEC common stock held. We have prepared on that basis the information contained in this joint proxy statement/prospectus concerning the number of shares of PAETEC Holding common stock expected to be issued in the mergers or issuable upon the exercise of options, warrants or other rights following the mergers. As described in this joint proxy statement/prospectus, however, PAETEC and US LEC may agree to adjust these exchange ratios on a proportionate basis to facilitate the listing of the PAETEC Holding common stock on the NASDAQ Global Market.

Questions and Answers About the Mergers

A:     We are delivering this document to you because it is a joint proxy statement being used by both the PAETEC and US LEC boards of directors to solicit proxies of PAETEC and US LEC stockholders in connection with the merger agreement, the mergers and the related transactions. In addition, this document is a prospectus being delivered to PAETEC and US LEC stockholders because PAETEC Holding is offering shares of its common stock to be issued in exchange for shares of PAETEC common stock and US LEC common stock if the mergers are completed.

A:     The special meeting of PAETEC stockholders will take place at          , Eastern Standard Time, on                      , 200    , in the          located at                      .

The special meeting of US LEC stockholders will take place at          , Eastern Standard Time, on                      , 200    , in the         located at                      .

Additional information relating to the PAETEC and US LEC special meetings is located beginning on pages 131 and 135, respectively.

A:     Before entering into the merger agreement, PAETEC formed a new Delaware corporation, PAETEC Holding. PAETEC Holding, in turn, created two wholly-owned subsidiaries, WC Acquisition Sub P Corp. and WC Acquisition Sub U Corp. When the transaction is completed, PAETEC Holding’s newly-created wholly-owned subsidiary, WC Acquisition Sub P Corp., will merge with and into PAETEC and PAETEC Holding’s other newly-created wholly-owned subsidiary, WC Acquisition Sub U Corp., will merge with and into US LEC. As a result of these two mergers, PAETEC and US LEC will become wholly-owned subsidiaries of PAETEC Holding. We refer to the two mergers as the “mergers,” to the merger of WC Acquisition Sub P Corp. with and into PAETEC as the “PAETEC merger” and to the merger of WC Acquisition Sub U Corp. with and into US LEC as the “US LEC merger.” The following diagram shows our corporate structure following completion of the mergers.

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Additional information on the mergers is located beginning on page 140.

Subject to US LEC obtaining the required stockholder vote and immediately before the effective time, a restated certificate of incorporation of PAETEC Holding will become effective. We refer to the proposal to the US LEC stockholders to approve the restated certificate of incorporation, including the six sub-proposals, as the “charter amendment proposal.” Approval of the charter amendment proposal is a condition to completion of the mergers.

Additional information on the charter amendment proposal is located beginning on page 266.

Before completion of the mergers, subject to US LEC obtaining the required stockholder vote, PAETEC Holding will adopt the PAETEC Holding Corp. 2006 Omnibus Incentive Plan that will be in effect if the mergers are completed. We refer to this incentive plan as the “new equity plan” and to the proposal to the US LEC stockholders to approve the new equity plan as the “new equity plan” proposal. Approval of the new equity plan is not a condition to completion of the mergers.

Additional information on the new equity plan proposal is located beginning on page 271.

A:     As a result of the mergers, each PAETEC stockholder is currently expected to receive 1.623 shares of PAETEC Holding common stock for each share of PAETEC common stock held, which we refer to as the “PAETEC exchange ratio.” Each US LEC stockholder is currently expected to receive 1.000 share of PAETEC Holding common stock for each share of US LEC common stock held, which we refer to as the “US LEC exchange ratio.” As described in this joint proxy statement/prospectus, PAETEC and US LEC may agree to adjust these exchange ratios on a proportionate basis to facilitate the listing of the shares of PAETEC Holding common stock on the NASDAQ Global Market. Stockholders of PAETEC and US LEC will receive cash in lieu of fractional shares.

Additional information on the consideration to be received in the mergers is located beginning on page 205.

A:     In connection with the mergers, US LEC has entered into the US LEC preferred stock repurchase agreement to repurchase its outstanding preferred stock, including accrued and unpaid dividends on these shares, for cash at a purchase price that will reflect a $30 million discount from the “liquidation value” of these shares at the effective time. The “liquidation value” will equal the sum of the stated value of these shares plus all accrued and unpaid dividends on these shares on the closing date of the mergers. If the closing date of the mergers were to occur as of the date of the PAETEC and US LEC special meetings, US LEC estimates that the liquidation value

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of the outstanding shares of US LEC preferred stock would be approximately $[296] million and the total purchase price for these shares would be approximately $[266] million. We refer to the repurchase of the US LEC preferred stock as the “US LEC preferred stock repurchase.” Completion of the US LEC preferred stock repurchase and completion of the mergers are each conditioned on the other.

Additional information on the US LEC preferred stock repurchase is located beginning on page 222.

A:     The US LEC preferred stock repurchase will permit US LEC to obtain a $30 million discount to the liquidation value of the US LEC preferred stock and to eliminate significant governance rights of the preferred stockholders, including their right to two seats on the US LEC board of directors and their right to consent to strategic transactions, changes in the US LEC chief executive officer or chief financial officer, increases to the size of the US LEC board of directors and modifications to the US LEC certificate of incorporation or bylaws. It will also eliminate the need for US LEC to arrange financing for the redemption of the US LEC preferred stock at the then liquidation value if the US LEC preferred stock were to remain outstanding in April 2010 or at 101% of the then liquidation value in the event of a “change of control,” as defined in the US LEC certificate of incorporation.

A:     PAETEC and US LEC believe that the combination will provide substantial strategic and financial benefits to their stockholders, including:

Additional information on the reasons for the mergers is located beginning on page 146 for PAETEC and on page 167 for US LEC.

A:     Assuming that the numbers of shares of PAETEC common stock and US LEC common stock outstanding immediately before the mergers are the same as the numbers of shares outstanding on September 30, 2006, we expect that approximately 80.9 million shares of PAETEC Holding’s common stock will be issued in connection with the mergers, of which former PAETEC common stockholders will own approximately 61% and former US LEC common stockholders will own approximately 39%. The merger agreement provides that options, restricted stock units, warrants and other PAETEC and US LEC rights may result in the issuance of additional shares of the new company’s common stock. As of September 30, 2006, 34.8 million of these additional shares would be issuable to former PAETEC securityholders and 8.2 million of these additional shares would be issuable to former US LEC securityholders, assuming satisfaction as of that date of the applicable vesting, exercise price payment and other conditions to which many of these issuances are subject. If all of these additional shares are issued, former PAETEC securityholders would own approximately 67.6% and former US LEC securityholders would own approximately 32.4% of the new company’s common stock.

A:     Yes.

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Under the PAETEC voting agreements, Madison Dearborn and Blackstone, which collectively own approximately 19.5% of the shares of PAETEC common stock entitled to vote at the PAETEC special meeting, have agreed to vote their shares in favor of adoption of the merger agreement and approval of the PAETEC merger. For a description of the PAETEC voting agreements, see “The PAETEC Voting Agreements” beginning on page 224. The PAETEC voting agreements are attached to this joint proxy statement/prospectus as Annexes C-1 and C-2.

Pursuant to the US LEC preferred stock repurchase agreement, Bain and THL, which at the record date for the US LEC special meeting collectively owned approximately         % of the voting power of the shares of US LEC common stock and preferred stock entitled to vote at the US LEC special meeting, have agreed to vote their shares in favor of adoption of the merger agreement and approval of the US LEC merger, as well as in favor of approval of the charter amendment proposal and the new equity plan. For a description of the US LEC preferred stock repurchase agreement, see “The US LEC Preferred Stock Repurchase Agreement” beginning on page 222. The US LEC preferred stock repurchase agreement is attached to this joint proxy statement/prospectus as Annex B.

A:     The affirmative vote of a majority of the shares of PAETEC common stock outstanding and entitled to vote as of the PAETEC record date is required to adopt the merger agreement and approve the PAETEC merger. If you abstain or fail to vote your shares in favor of adoption of the merger agreement and approval of the PAETEC merger, this will have the same effect as voting your shares against the merger proposal.

As noted above, under the PAETEC voting agreements, Madison Dearborn and Blackstone, which at the record date for the PAETEC special meeting collectively owned approximately 19.5% of the shares of PAETEC common stock entitled to vote at the PAETEC special meeting, have agreed to vote their shares in favor of adoption of the merger agreement and approval of the PAETEC merger. Also at the close of business on the record date for the PAETEC special meeting, directors and executive officers of PAETEC had the power to vote an additional approximately 14.7% of the then outstanding shares of PAETEC common stock and each has indicated his present intention to vote, or cause to be voted, the shares of PAETEC common stock over which he has voting power in favor of adoption of the merger agreement and approval of the PAETEC merger.

A:     The affirmative vote of the holders of a majority of the voting power of the shares of US LEC common stock and US LEC preferred stock outstanding and entitled to vote as of the US LEC record date, voting together as a single class, is required to adopt the merger agreement and approve the US LEC merger. Each share of US LEC common stock has one vote and each share of US LEC preferred stock has approximately [36.1] votes, because the preferred stock entitles its holder to one vote per share of US LEC common stock into which the preferred stock may be converted as of the US LEC record date. If you abstain or fail to vote your shares in favor of adoption of the merger agreement and approval of the US LEC merger, this will have the same effect as voting your shares against the merger proposal.

As noted above, under the US LEC preferred stock repurchase agreement, Bain and THL, which at the record date for the US LEC special meeting collectively owned approximately          % of the voting power of the shares of US LEC common stock and preferred stock entitled to vote at the US LEC special meeting, have agreed to vote their shares in favor of adoption of the merger agreement and approval of the US LEC merger. Also at the record date for the US LEC special meeting, directors and executive officers of US LEC other than those affiliated with Bain and THL had the power to vote an additional approximately          % of the then outstanding voting power of the shares of US LEC common stock and US preferred stock and each has indicated his present

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intention to vote, or cause to be voted, the shares of US LEC common stock and US LEC preferred stock over which he has the power to vote in favor of adoption of the merger agreement and approval of the US LEC merger.

A:     No vote is required by the PAETEC stockholders to approve the charter amendment proposal.

The affirmative vote of the holders of a majority of the voting power of the shares of US LEC common stock and US LEC preferred stock outstanding and entitled to vote as of the US LEC record date, voting together as a single class, is required to approve the charter amendment proposal, including each of the six sub-proposals of that proposal. Each share of US LEC common stock has one vote and each share of US LEC preferred stock has approximately [36.1] votes, because the preferred stock entitles its holder to one vote per share of US LEC common stock into which the preferred stock may be converted as of the US LEC record date. If you abstain or fail to vote your shares in favor of approval of the charter amendment proposal, including as to any of the six sub-proposals of the charter amendment proposal, this will have the same effect as voting your shares against approval of the charter amendment proposal. In addition, since completion of the mergers is conditioned upon approval of the charter amendment proposal, a failure to vote your shares in favor of the proposal will have the same effect as voting against approval of the US LEC merger.

As noted above, under the US LEC preferred stock repurchase agreement, Bain and THL, which at the record date for the US LEC special meeting collectively owned approximately [24.7]% of the voting power of the shares of US LEC common stock and preferred stock entitled to vote at the US LEC special meeting, have agreed to vote their shares in favor of approval of the charter amendment proposal. Also at the record date for the US LEC special meeting, directors and executive officers of US LEC other than those affiliated with Bain and THL had the power to vote an additional approximately [31.9]% of the then outstanding voting power of the shares of US LEC common stock and US LEC preferred stock and each has indicated his present intention to vote, or cause to be voted, the shares of US LEC common stock and US LEC preferred stock over which he has the power to vote in favor of approval of the charter amendment proposal.

A:     No vote is required by the PAETEC stockholders to approve the new equity plan.

Assuming a quorum is present at the US LEC special meeting, the affirmative vote of the holders of a majority of the voting power of the shares of US LEC common stock and US LEC preferred stock present in person or represented by proxy at the US LEC special meeting and entitled to vote on the new equity plan, voting together as a single class, is required to approve the new equity plan. Each share of US LEC common stock has one vote and each share of US LEC preferred stock has approximately [36.1] votes, because the preferred stock entitles its holder to one vote per share of US LEC common stock into which the preferred stock may be converted as of the US LEC record date. If you abstain or fail to vote your shares in favor of approval of the new equity plan, this will have the same effect as voting your shares against approval of this proposal. Since completion of the mergers is not conditioned upon approval of the new equity plan, a vote against approval of the new equity plan will not affect the obligation of PAETEC and US LEC to complete the mergers if the other closing conditions are satisfied.

As noted above, under the US LEC preferred stock repurchase agreement, Bain and THL, which at the record date for the US LEC special meeting collectively owned approximately [24.7]% of the voting power of the shares of US LEC common stock and preferred stock entitled to vote at the US LEC special meeting, have agreed to vote their shares in favor of approval of the new equity plan. Also at the record date for the US LEC special meeting, directors and executive officers of US LEC other than those affiliated with Bain and THL had the power to vote an additional approximately [31.9]% of the then outstanding voting power of the shares of US LEC

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common stock and US preferred stock and each has indicated his present intention to vote, or cause to be voted, the shares of US LEC common stock and US LEC preferred stock over which he has the power to vote in favor of approval of the new equity plan.

A:     Neither PAETEC nor US LEC has paid any cash dividends on its capital stock and PAETEC Holding does not anticipate paying any cash dividends on its common stock for the foreseeable future after completion of the mergers.

A:     It is a condition to the completion of the mergers that the common stock of PAETEC Holding, including the shares issuable pursuant to the mergers, be approved for listing on the NASDAQ Global Market or, if listing of the PAETEC Holding common stock on the NASDAQ Global Market is not reasonably practicable, on the NASDAQ Capital Market. We have applied to list the PAETEC Holding common stock on the NASDAQ Global Market under the trading symbol “CLEC.”

A:     Upon completion of the mergers, Arunas A. Chesonis, who currently serves as PAETEC’s Chairman of the Board, President and Chief Executive Officer, will become Chairman of the Board and Chief Executive Officer of PAETEC Holding, and Richard T. Aab, who currently serves as US LEC’s Chairman of the Board, will become Vice Chairman of the Board of PAETEC Holding. PAETEC Holding’s board of directors will initially consist of nine members, six of whom have been or will be designated by PAETEC and will include all five existing PAETEC directors, and three of whom have been designated by US LEC from among the existing US LEC directors.

Additional information about the PAETEC Holding directors is located beginning on page 247.

A:     After carefully reading and considering the information contained in this joint proxy statement/prospectus, please complete and sign your proxy card and return it in the enclosed postage-paid envelope as soon as possible so that your shares may be represented at your special meeting. To ensure that your vote is recorded, please vote your proxy as instructed on your proxy card even if you currently plan to attend your special meeting in person. You may also cast your vote by telephone or Internet by following the instructions on your proxy card. Please do not send in your PAETEC or US LEC share certificates now. After the mergers are completed, you will receive instructions as to what to do with your share certificates.

Additional information on voting procedures is located beginning on page 132 for PAETEC and on page 137 for US LEC.

A:     If you vote by telephone, by Internet, or by completing, signing, dating and returning your signed proxy card, your proxy will be voted in accordance with your instructions. If you sign, date, and send your proxy and do not indicate how you want to vote, your shares will be voted FOR adoption of the merger agreement and approval of the mergers and, in the case of US LEC stockholders, FOR approval of the charter amendment proposal and the new equity plan.

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A:     Yes. If you are a stockholder of record of PAETEC common stock at the close of business on                      , 2006 or of US LEC common stock or preferred stock at the close of business on                      , 2006, you may attend your special meeting and vote your shares in person, in lieu of submitting your proxy by telephone, Internet or returning your signed proxy card.

A:     Admittance to the special meetings is limited to stockholders of record of PAETEC or US LEC, as the case may be, or their authorized representatives. If you wish to attend your special meeting, bring your proxy or your voter information form. You must also bring photo identification.

A:     This means you own shares of both PAETEC and US LEC or you own shares of PAETEC or US LEC that are registered under different names. For example, if you are a US LEC stockholder, you may own some shares directly as a stockholder of record and other shares through a broker or you may own shares through more than one broker. In these situations, you will receive multiple sets of proxy materials. You must vote, sign and return all of the proxy cards or follow the instructions for any alternative voting procedure on each of the proxy cards you receive in order to vote all of the shares you own. Each proxy card you receive will come with its own postage-paid return envelope; if you vote by mail, make sure you return each proxy card in the return envelope that accompanied that proxy card.

A:     Send a later-dated, signed proxy card before the date of your special meeting so that it is received before your special meeting or attend your company’s special meeting in person and vote. You may also revoke your proxy card by sending a notice of revocation that is received before your special meeting to your company’s Corporate Secretary at the address under “Summary—The Companies” beginning on page 15. You may also change your vote by telephone or Internet. You may change your vote by using any one of these methods regardless of the procedure used to cast your previous vote.

Additional information on changing your vote is located on page 133 for PAETEC and on page 138 for US LEC.

A:     If you do not provide your broker with instructions on how to vote your “street name” US LEC shares, your broker will not be permitted to vote them at the US LEC special meeting. You should therefore be sure to provide your broker with instructions on how to vote your shares. US LEC stockholders should check the voting form used by their brokers to see if their broker offers telephone or Internet voting.

If you do not give voting instructions to your broker, your US LEC shares will be counted towards a quorum at the US LEC special meeting, but effectively will be treated as voting against adoption of the merger agreement and approval of the US LEC merger and against approval of the charter amendment proposal, unless you appear and vote in person at your special meeting. Such a broker non-vote will not affect the vote by US LEC stockholders on approval of the new equity plan. If your broker holds your US LEC shares and you plan to attend and vote at the US LEC special meeting, please bring a letter from your broker identifying you as the beneficial owner of the shares and authorizing you to vote.

Information on changing how to vote if your US LEC shares are held in street name is located on page 138.

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A:     No. If the mergers are completed, we will send former stockholders of both PAETEC and US LEC written instructions for exchanging their share certificates. PAETEC Holding shares will be in uncertificated book-entry form unless a physical certificate is requested by the holder.

A:     PAETEC, US LEC and PAETEC Holding are working to complete the mergers by [            ], although we cannot assure completion by any particular date.

A:     Yes. Subject to compliance with requirements of Delaware law, a PAETEC stockholder may dissent from the adoption of the merger agreement and approval of the transactions contemplated by the merger agreement and have the fair value of the stockholder’s shares of PAETEC common stock determined by a court. To exercise appraisal rights, a PAETEC stockholder must strictly comply with all of the applicable requirements of Delaware law summarized under “The Mergers—Dissenters’ or Appraisal Rights”. A copy of Section 262 of the General Corporation Law of the State of Delaware, which governs appraisal rights, is included as Annex H to this joint proxy statement/prospectus.

A:     No. Under Delaware law, US LEC stockholders will not have appraisal rights in connection with the issuance of PAETEC Holding common stock pursuant to the US LEC merger.

A:     Every vote is important. PAETEC and US LEC need your affirmative vote in favor of each of the proposals to be considered at the special meetings. If you abstain or fail to vote your PAETEC or US LEC shares in favor of adoption of the merger agreement and approval of the mergers or, in the case of US LEC stockholders, approval of the charter amendment proposal, this will have the same effect as voting your PAETEC or US LEC shares against these proposals.