<PAGE>   1

                                                                   EXHIBIT 10.29


                                                                April 1, 2001

                                                            |__| Employee's Copy
                                                            |__| Employer's Copy

                               RETENTION AGREEMENT

To William L. Collins, III:

         Metrocall, Inc. (the "Company") wants to retain your services and to
give you additional incentives to assist in the restructuring of the Company,
including a possible "Change in Control" of the Company, should the Company
decide to pursue any such transaction.

         RETENTION PAYMENT. To provide you with special incentives to remain
with the Company, the Company will pay you an amount equal to (1) your annual
Base Salary as currently in effect, and (2) your target annual bonus amount for
the current fiscal year as approved by the Company's Board of Directors (the
"Board")(the "Retention Payment"), reduced by any applicable withholding taxes.
The Company will pay you the Retention Payment in a lump sum, in cash or
immediately available funds, not later than April 16, 2001. You hereby
acknowledge and agree that this Retention Payment is in lieu of any retention
payments pursuant to the Company's Key Employee Retention Plan.

         You agree to repay the "Retention Repayment Amount" (defined to mean
the Retention Payment, net of taxes paid and/or withheld) within 10 days after
your employment ends if your employment ends prior to the earliest of (1) the
entry by a court of competent jurisdiction of an order confirming a plan of
reorganization of the Company under Chapter 11 of the Bankruptcy Code; (2) a
sale or transfer of all or substantially all of the assets of the Company; (3) a
decree or order by a court of competent jurisdiction appointing a trustee (or
other similar official) of the Company; or (4) two years from the date hereof.
Notwithstanding the foregoing, the Company will forgive repayment of 100% of the
Retention Repayment Amount if you (w) resign for Good Reason, (x) the Company
ends your employment without Cause, (y) you die, or (z) your employment ends
under a Disability.

         For purposes of this Agreement, "Change of Control", "Good Reason",
"Cause" and "Disability" shall have the meanings contained in the Change of
Control Agreement between you and the Company dated as of May 15, 1996, as
amended as of the date hereof or as amended or replaced in the future (the
"Change of Control Agreement").

         REPAYMENT.  You agree to make any repayments provided under this
Agreement to the Company or its successor.

         DUTIES. As part of this Agreement, you agree to (i) continue to perform
all of your current duties and comply with your employment agreement with the
Company, as any such agreement exists today or is amended or replaced in the
future (the "Employment Agreement"); (ii) assist with various non-operating
activities, which could include outside investment, financing, transactions, or
business reconfiguration as the Company requests, including

<PAGE>   2

providing all information the Company considers necessary or appropriate; (iii)
carry out any other tasks the Company reasonably requests to facilitate such
activities or any restructuring or Change in Control; and (iv) perform the
duties assigned to you following any such activities, including any
restructuring or Change in Control.

         AMENDMENT; WAIVER. Neither you nor the Company may modify, amend, or
waive the terms of this Agreement other than by a written instrument signed by
you and an executive officer of the Company, with the prior approval of the
Board. Either party's waiver of the other's compliance with any provision of
this Agreement does not waive any other provision of this Agreement or any
subsequent breach by such party of a provision of this Agreement.

         NO MITIGATION OR OFFSET. You are not required to mitigate the payments
under this Agreement, and the Company will not offset its obligations under this
Agreement to reflect compensation you receive from other employers.

         GOVERNING LAW. The laws of the state in which your principal place of
employment lies (other than its conflict of laws provisions) govern this
Agreement.

         ASSIGNMENT. This Agreement binds the Company, its successors or
assigns, and your heirs and the personal representatives of your estate. Without
the Company's prior written consent, you may not assign or delegate this
Agreement or any or all rights, duties, obligations, or interests under it. You
agree that the assumption of this Agreement by a successor releases the Company,
except to the extent it is part of the successor, from any obligations under
this Agreement, including any retention payments, and you further release and
waive any claims you may have against the Company, except to the extent it is
part of the successor, for the payment of such amounts.

         EFFECTS ON EMPLOYMENT OR OTHER RELATIONSHIP. Nothing in this Agreement
restricts the Company's rights or those of any of its affiliates to terminate
your employment or other relationship at any time, with or without Cause.

         NOTICES. Notices must be given in writing by personal delivery, by
certified mail, return receipt requested, by telecopy, or by overnight delivery.
You should send or deliver your notices to the Company's corporate headquarters,
addressed to the chair of the Compensation Committee of the Board. The Company
will send or deliver any notice given to you at your address as reflected on the
Company's personnel records. You and the Company may change the address for
notice by like notice to the other. You and the Company agree that notice is
received on the date it is personally delivered, the date it is received by
certified mail, the date of guaranteed delivery by the overnight service, or the
date the fax machine confirms effective transmission.





                                       2
<PAGE>   3


If you accept the terms of this Agreement, please sign below. We encourage you
to consult with any advisors you choose.

                                        METROCALL, INC.


                               By:      /s/FRANCIS A. MARTIN, III
                                 -----------------------------------------------
                                        Francis A. Martin, III
                                        Chairman of the Compensation Committee


I accept and agree to the terms set forth in this Agreement:

     /s/WILLIAM L. COLLINS, III
-----------------------------------
       William L. Collins, III                       Dated:
                                                           -------------------


                                       3