<PAGE>

                                                               Exhibit 10.24.1
                         REGISTRATION RIGHTS AGREEMENT
                         -----------------------------

          THIS AGREEMENT is made and entered into as of December 8, 1999, among
PaeTec Corp., a Delaware corporation (the "Company"), and the persons and
entities listed on the attached Schedule I (the "Purchasers").
                                ----------

                                    RECITALS
                                    --------

          WHEREAS, Star Telecommunications, Inc., a Delaware corporation (the
"Seller"), owns 850,000 shares of Class A Common Stock, par value $0.01 per
share (the "Class A Common Stock"), of the Company;

          WHEREAS, the Seller is selling to the Purchasers and the Purchasers
are purchasing from the Seller all of such 850,000 shares (the "Purchased
Shares"), in the amounts set forth on Schedule I hereto, concurrently with the
                                      ----------
execution and delivery of this Agreement and pursuant to the terms and
conditions of a Common Stock Purchase Agreement, dated as of December 6, 1999,
between the Purchasers and the Seller (the "Stock Purchase Agreement");

          WHEREAS, the Company granted to the Seller certain piggy-back
registration rights with respect to the Purchased Shares in connection with the
original issuance thereof to the Seller; and

          WHEREAS, the Company desires to grant to each Purchaser certain piggy-
back registration rights with respect to (i) the Purchased Shares held by such
Purchaser and (ii) any shares of common stock of the Company paid, issued or
distributed in respect of such Purchased Shares by way of stock dividend or
distribution or stock split or in connection with a combination of shares,
recapitalization or otherwise (the shares referred to in clauses (i) and (ii)
collectively, the "Registrable Shares") according to the terms and provisions of
this Agreement;

          NOW, THEREFORE, in consideration of the foregoing, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

1.  Piggy-Back Registration Rights.
--  ------------------------------

          (a) If at any time or from time to time after the completion of the
initial public offering of shares of the Class A Common Stock, the Company shall
determine to register any of its equity securities, either for its own account
or the account of a security holder or holders (other than a registration of
securities on Form S-8 relating solely to employee benefit or stock plans or a
registration
<PAGE>

on Form S-4 to effect a merger or other reorganization), the Company shall
promptly give to the Purchasers written notice thereof and, upon the written
request of a Purchaser made within 10 business days after receipt of such
written notice from the Company, and subject to paragraph (b) below, shall
include in such registration (and any related qualification under blue sky laws
or other compliance), and in any underwriting involved therein, all the
Registrable Shares held by such Purchaser specified in such written request.

          (b) If the registration of which the Company gives notice is for a
registered public offering for the account of the Company or a security holder
(such security holder, an "Initiating Holder") involving an underwriting, the
Company shall so advise the Purchasers as a part of the written notice given to
the Purchasers pursuant to Section 1(a).  In such event the right of any
Purchaser to registration pursuant to this Section 1 shall be conditioned upon
such Purchaser's participation in such underwriting, and the inclusion of
Registrable Shares held by such Purchaser in the underwriting shall be limited
to the extent provided herein.  Each Purchaser desiring to participate in such
an offering (together with the Company and the other security holders
distributing their securities through such underwriting) shall enter into an
underwriting agreement in customary form with the managing underwriter selected
for such underwriting by the Company.  Notwithstanding any other provision of
this Section 1, if the managing underwriter determines that marketing factors
require a limitation of the number of shares to be underwritten, the managing
underwriter may exclude some or all of the Registrable Shares or securities of
other holders of registration rights granted by the Company from such
registration in accordance with the succeeding sentence.  In such event and
provided the managing underwriter has so notified the Company in writing, the
securities to be included in such offering shall consist of (i) first, any
securities the Company or the Initiating Holder, as the case may be, proposes to
sell, and (ii) second, the number of Registrable Shares the Purchasers requested
to be included in such registration that, in the opinion of the managing
underwriter, can be sold without jeopardizing the success of the offering of all
the securities that the Company or the Initiating Holder, as the case may be,
desires to sell for its own account, such amount to be allocated on a pro rata
basis among the Purchasers who have requested their securities be so included
based on the number of Registrable Shares that each Purchaser has requested to
be so included; provided that, in the event another person has duly requested
pursuant to an agreement with the Company that the Company register other
securities of the Company and such request has not been withdrawn, the
Purchasers and such other person shall be included in such registration pro rata
based on the number of securities the Purchasers and such other person have
requested to be so included.  If any Purchaser disapproves of the terms of any
such underwriting, such Purchaser may elect to withdraw therefrom by written
notice to the Company and the managing underwriter.  Any securities excluded or
withdrawn from such underwriting shall be withdrawn from such registration, and
shall continue to be subject to the terms of this Agreement.

                                       2
<PAGE>

          (c) The Company shall have the right to terminate or withdraw any
registration initiated by it under this Section 1 prior to the effectiveness of
such registration whether or not any Purchaser has elected to include securities
in such registration; provided, however, that any such termination or withdrawal
shall not relieve the Company from its obligation to pay expenses of the
Purchasers pursuant to Section 1(d).

          (d) All expenses associated with any registration hereunder
(including, without limitation, registration, qualification and filing fees,
printing expenses, blue sky fees, and fees and disbursements of counsel and
accountants for the Company) shall be borne by the Company.  Notwithstanding the
foregoing, the Company shall not be obligated to pay any fees or disbursements
of counsel to any Purchaser, and underwriters' discounts and commissions shall
be borne by the participating Purchasers pro rata in proportion to the number of
securities being registered.

               (e) In the case of each registration under this Section 1, the
Company shall:

                   (i) prepare and file with the Securities and Exchange
Commission a registration statement with respect to such securities and use its
best efforts to cause such registration statement to become and remain effective
for at least 45 days or until the distribution described in the registration
statement has been completed, whichever first occurs (provided that before
filing a registration statement or prospectus or any amendments or supplements
thereto, the Company shall furnish to a single counsel to the Purchasers copies
of all such documents proposed to be filed, which documents shall be subject to
the review and, as to any information relating to the Purchasers or the proposed
plan of distribution of the Registrable Shares, comment of such counsel);

                   (ii) furnish to participating Purchasers such reasonable
number of copies of the registration statement, preliminary prospectus, final
prospectus and such other documents as such Purchasers may reasonably request in
order to facilitate the public offering of the Registrable Shares included in
such registration;

                   (iii)  use its best efforts to register and qualify the
securities covered by such registration statement under such other securities or
blue sky laws of such jurisdictions as shall be reasonably requested by
participating Purchasers, to take all actions which may be reasonably necessary
to keep such registration or qualification in effect for so long as such
registration statement remains in effect, and take any other action which may be
reasonably necessary or advisable to enable the Purchasers to consummate the
disposition in such jurisdictions of the Registrable Shares included in such
registration, provided that the Company shall not be required in connection
therewith or as a condition thereto

                                       3
<PAGE>

to qualify as a foreign corporation or as a dealer in securities or to file a
general consent to service of process in any such states or jurisdictions in
which it has not already done so and except as may be required by the Securities
Act of 1933, as amended (the "Securities Act");

                   (iv) immediately notify the Purchasers at any time when the
Company becomes aware that a prospectus relating thereto is required to be
delivered under the Securities Act, of the happening of any event as a result of
which the prospectus included in such registration statement, as then in effect,
includes an untrue statement of a material fact or omits to state any material
fact required to be stated therein or necessary to make the statements therein
not misleading in the light of the circumstances under which they were made, and
at the request of the Purchasers promptly prepare and furnish to the Purchasers
a reasonable number of copies of a supplement or an amendment of such prospectus
as may be necessary so that, as thereafter delivered to the purchasers of such
securities, such prospectus shall not include an untrue statement of a material
fact or omit to state a material fact required to be stated therein or necessary
to make the statements therein not misleading in the light of the circumstances
under which they were made;

                   (v) provide a transfer agent and registrar for all
Registrable Shares covered by such registration statement no later than the
effective date of such registration statement; and

                   (vi) list all Registrable Shares covered by such registration
statement on any securities exchange on which any of the same class of common
stock of the Company is then listed.

          (f) The Company shall indemnify participating Purchasers and each
person, if any, who controls such Purchasers within the meaning of the
Securities Act against all expenses, claims, losses, damages or liabilities (or
actions in respect thereof), arising out of or based on any untrue statement (or
alleged untrue statement) of a material fact contained in any registration
statement or prospectus, or any amendment or supplement thereto, incident to any
such registration, or based on any omission (or alleged omission) to state
therein a material fact required to be stated therein or necessary to make the
statements therein, in the light of the circumstances in which they were made,
not misleading, and the Company shall reimburse such Purchasers for any legal
and any other expenses reasonably incurred, as such expenses are incurred, in
connection with investigating, preparing or defending any such claim, loss,
damage, liability or action, provided that the Company shall not be liable in
any such case to the extent that any such claim, loss, damage, liability or
expense arises out of or is based on any untrue statement or omission, or
alleged untrue statement or omission, made in reliance upon and in conformity
with written information relating to a Purchaser

                                       4
<PAGE>

furnished to the Company or any underwriter by such Purchaser for inclusion in
any registration statement or prospectus, or any amendment or supplement
thereto.

          (g) Each Purchaser shall, if Registrable Shares held by such Purchaser
are included in the securities as to which such registration is being effected,
indemnify the Company, each of its directors and officers, each underwriter, if
any, of the Company's securities covered by such a registration statement and
each person, if any, who controls the Company or such underwriter against all
claims, losses, damages and liabilities (or actions in respect thereof) arising
out of or based on any untrue statement (or alleged untrue statement) of a
material fact contained in any such registration statement or prospectus, or any
amendment or supplement thereto, incident to any such registration, or based on
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein, in the light of
the circumstances in which they were made, not misleading, and shall reimburse
the Company, such directors, officers, underwriters and control persons for any
legal or any other expenses reasonably incurred, as such expenses are incurred,
in connection with investigating or defending any such claim, loss, damage,
liability or action, in each case to the extent, but only to the extent, that
such untrue statement (or alleged untrue statement) or omission (or alleged
omission) is made in such registration statement or prospectus, or in such
amendment or supplement thereto, in reliance upon and in conformity with written
information relating to such Purchaser furnished to the Company or any
underwriter by such Purchaser for inclusion therein; provided that the
obligations to indemnify shall be individual, not joint and several, for each
Purchaser and shall be limited to the net amount of proceeds received by such
Purchaser from the sale of Registrable Shares pursuant to such registration
statement.

          (h) If for any reason the indemnity set forth in paragraphs (f) or (g)
above is unavailable or insufficient to hold harmless an indemnified party in
respect of any losses, claims, damages, liabilities or expenses (or actions in
respect thereof), then the indemnifying party shall contribute to the amount
paid or payable by the indemnified party as a result of such losses, claims,
damages, liabilities or expenses (or actions in respect thereof) in such
proportion as is appropriate to reflect the relative fault of the indemnifying
party on the one hand and the indemnified party on the other hand in connection
with statements or omissions which resulted in such losses, claims, damages,
liabilities or expenses (or actions in respect thereof), as well as any other
relevant equitable considerations, subject to the liability limitations set
forth in the proviso in the last sentence of paragraph (g) above.  The relative
fault shall be determined by reference to, among other things, whether the
untrue or alleged untrue statement of a material fact or the omission or alleged
omission to state a material fact relates to information supplied by the
indemnifying party or the indemnified party and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
untrue statement or omission.  Notwithstanding the foregoing, a

                                       5
<PAGE>

Purchaser shall not be required to contribute any amount in excess of the amount
it would have been required to pay to an indemnified party if the indemnity
under paragraph (g) hereof were available. No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any person who was not guilty of such
fraudulent misrepresentation.

          (i) The provisions on indemnification and contribution contained in
any underwriting agreement entered into in connection with any underwritten
registration referred to in this Agreement shall supersede the provisions of
paragraphs (f), (g) and (h) above with respect to the parties to such
underwriting agreement.

          (j) Each Purchaser shall furnish to the Company such information
regarding such Purchaser, the Registrable Shares held by such Purchaser, the
distribution proposed by such Purchaser and such other information as shall be
required by the Securities Act or the rules promulgated thereunder as the
Company may reasonably request in writing and as shall be reasonably required in
connection with any registration referred to in this Agreement.

          (k) The registration rights granted to each Purchaser in this Section
1 shall expire as to such Purchaser at such time (if ever) as such Purchaser may
sell the Registrable Shares held by such Purchaser under Rule 144 promulgated
under the Securities Act (or any successor thereto) without limitation as to
volume.  The foregoing notwithstanding, a Purchaser's registration rights under
this Section 1 shall expire after the Company has offered such Purchaser the
cumulative opportunity to register all of such Purchaser's Registrable Shares in
two registered offerings, irrespective of whether such Purchaser elects to
participate in such registered offerings.

          2.  Lock-Up.  Each Purchaser hereby agrees, if so requested in writing
              -------
by any managing underwriter of an underwritten registration by the Company of
its securities (either for its own account, or for the benefit of the holders of
any securities of the Company), not to effect any sale or distribution of
Registrable Shares, except as part of such underwritten registration, during the
seven days prior to and the 90 days (or 180 days, in the case of the Company's
initial public offering) after the time such underwritten registration has
become effective or such period of time shorter than 90 days (or 180 days, as
applicable) that is sufficient and appropriate, in the opinion of the managing
underwriter, in order to complete the sale and distribution of securities
included in such underwritten registration; provided, however, that if any
director or executive officer of the Company or any owner of 5% or more of the
outstanding common stock of the Company subject to such a lock-up restriction is
subject to a lock-up restriction of shorter duration, such shorter lock-up
period shall apply to such Purchaser.  If requested, each Purchaser shall enter
into a lock-up agreement with

                                       6
<PAGE>

the applicable underwriters that is consistent with the agreement in the
preceding sentence.  The provisions of this Section 2 with respect to any
underwritten registration shall not limit the exercise by the Purchasers of
their rights under Section 1 with respect to such underwritten registration.

          3.  Miscellaneous.
              -------------

(a)  This Agreement may be modified or amended only upon the written consent of
     the Company and the Purchasers holding a majority of the then-outstanding
     Registrable Shares; provided, however, that no modification or amendment of
     this Agreement that adversely affects the rights hereunder of any Purchaser
     in any material respect shall be effective against such Purchaser unless
     such Purchaser shall have consented in writing to such modification or
     amendment.

          (b) This Agreement shall be interpreted under and governed by the laws
of the State of New York applicable to agreements made and to be performed
entirely within the State of New York, without giving effect to the principles
of conflicts of law thereunder.

          (c) This Agreement shall be binding upon and inure to the benefit of
the parties hereto and their respective successors and permitted assigns.  No
Purchaser shall be permitted to assign any of its registration rights or other
rights under this Agreement to any other person without the prior written
consent of the Company, which may be granted or withheld by the Company in its
sole discretion.  Any permitted assignee of registration rights hereunder shall
execute and agree to be bound by, and shall be deemed a "Purchaser" under, this
Agreement.

          (d) This Agreement may be executed in counterparts, each of which
shall be an original but all of which shall constitute one and the same
instrument.

          (e) Any notice, demand or other communication required, permitted or
desired to be given hereunder shall be in writing and shall be deemed
effectively given upon personal delivery, facsimile transmission (with
confirmation of receipt), delivery by reputable overnight service or five (5)
days following deposit in the United States mail (if sent by certified or
registered mail, postage prepaid, return receipt requested), in each case duly
addressed to the Company at its headquarters or to the Purchasers at the
respective addresses of the Purchasers listed on Schedule I hereto (unless the
                                                 ----------
Company receives notice pursuant to this Section 3(e) of a change to any such
address).

                                       7
<PAGE>

          (f) This agreement sets forth the entire understanding and agreement
of the parties with respect to its subject matter.



                  [remainder of page intentionally left blank;
                            signature pages follow]

                                       8
<PAGE>

          IN WITNESS WHEREOF, the parties have executed this Agreement on the
day and year first above written.

                              PURCHASERS:

                              GKW UNIFIED HOLDINGS LLC

                              By:  /s/ Gregg Ritchey
                                 ------------------------------------------
                              Its: CFO Manager
                                  -----------------------------------------

                              CAROLWOOD COMPANY LLC

                              By:  /s/ Lodwrick M. Cook
                                 ------------------------------------------
                              Its: Manager
                                  -----------------------------------------


                              KEPACA LLC


                              By:  /s/ Thomas J. Casey
                                 ------------------------------------------
                              Its: President
                                  -----------------------------------------


                              FIDUCIA INTERNATIONAL


                              By:  /s/ Gregg Ritchey
                                 ------------------------------------------
                              Its: General Partner
                                  -----------------------------------------

                              SAN PASQUAL CORP.


                              By:  /s/ David Lee
                                 ------------------------------------------
                              Its: General Partner
                                  -----------------------------------------


                              BARRY PORTER

                              By:  /s/ Barry Porter
                                 ------------------------------------------
                              Its:
                                  -----------------------------------------

                              THE WALKER LIVING TRUST

                              By:  /s/ Clint W. Walker
                                 ------------------------------------------
                              Its:  Trustee
                                  -----------------------------------------

                                       9
<PAGE>

                              ROSALIE ZALIS

                              By:  /s/Rosalie Zalis
                                 ------------------------------------------
                              Its:
                                  -----------------------------------------

                              PETE WILSON

                              By:  /s/ Pete Wilson
                                 ------------------------------------------
                              Its:
                                  -----------------------------------------


                              THE COMPANY:

                              PAETEC CORP.


                              By:  /s/ Timothy Bancroft
                                 ------------------------------------------
                              Its:  Vice President - Finance
                                  -----------------------------------------

                                       10
<PAGE>

                                   SCHEDULE I
                                   ----------
<TABLE>
<CAPTION>

       Buyer                              Shares
       -----                              -------
<S>                                       <C>

GKW Unified Holdings LLC                  360,000
360 N. Crescent
Beverly Hills, CA 90210

Kepaca LLC                                200,000
1476 Via Cresta
Pacific Palisades, CA  90272
Attention:  Tom Casey

Carolwood Company LLC                     100,000
13849 Weddington Street
Sherman Oaks, CA  91401
Attention:  Lodwrick Cook

Fiducia International                      50,000
16875 Callie De Sarah
Pacific Palisades, CA 90272
Attn: Gregg Ritchie

San Pasqual                                50,000
c/o The Management Group
9100 Wilshire Blvd., Suite 725E
Beverly Hills, CA  90212

Barry Porter                               50,000
c/o The Management Group
9100 Wilshire Blvd., Suite 725E
Beverly Hills, CA  90212

The Walker Living Trust                    30,000
2600 Via Segunda
Palos Verdes Estates, CA 90274
Attention:  Clint Walker

Rosalie Zalis                               5,000
360 N. Crescent Drive
Beverly Hills, CA  90274

Pete Wilson                                 5,000
360 N. Crescent Drive
Beverly Hills, CA  90274
</TABLE>