<PAGE>
Exhibit 99 to Schedule 13D
November 29, 2000
This will confirm the agreement by and among all of the undersigned that
the Schedule 13D filed on or about this date with respect to the beneficial
ownership of the undersigned of shares of the Class A Common Stock of TeleCorp
PCS, Inc. is being filed on behalf of each of the undersigned. This agreement
may be executed in two or more counterparts, each of which shall be deemed an
original, but all of which together shall constitute one and the same
instrument.
/s/ Thomas H. Sullivan
------------------------------
Thomas H. Sullivan
/s/ Gerald T. Vento
------------------------------
Gerald T. Vento
/s/ William M. Mounger, II
------------------------------
William M. Mounger, II
/s/ E.B. Martin, Jr.
------------------------------
E.B. Martin, Jr.
TELECORP INVESTMENT CORP., L.L.C.
By: /s/ Thomas H. Sullivan
--------------------------
Name: Thomas H. Sullivan
Title: Manager
TELECORP INVESTMENT CORP. II,
L.L.C.
By: /s/ Thomas H. Sullivan
--------------------------
Name: Thomas H. Sullivan
Title: Manager
<PAGE>
PRIVATE EQUITY INVESTORS III, L.P.
By: Rohit M. Desai Associates III, LLC, its
general partner
By: /s/ Robert M. Dean
---------------------------------
Name: Rohit M. Desai
Title: Managing Member
EQUITY-LINKED INVESTORS-II
By: Rohit M. Desai Associates-II, its general
partner
By: /s/ Rohit M. Desai
---------------------------------
Name: Rohit M. Desai
Title: Managing Member
ROHIT M. DESAI ASSOCIATES III, LLC
By: /s/ Rohit M. Desai
---------------------------------
Name: Rohit M. Desai
Title: Managing Member
ROHIT M. DESAI ASSOCIATES-II
By: /s/ Rohit M. Desai
---------------------------------
Name: Rohit M. Desai
Title: Managing Member
/s/ Rohit Desai
-------------------------------------
Rohit Desai
HCP CAPITAL FUND, L.P.
By: James M. Hoak & Co, its general partner
By: /s/ James Hoak
---------------------------------
Name: James Hoak
Title: Chairman
<PAGE>
HOAK COMMUNICATIONS PARTNERS, L.P.
By: HCP Investments, L.P., its general partner
By: Hoak Partners, LLC, its general partner
By: /s/ James Hoak
---------------------------------
Name: James Hoak
Title: Manager
JAMES M. HOAK & CO.
By: /s/ James Hoak
---------------------------------
Name: James Hoak
Title: Chairman
HCP INVESTMENTS, L.P.
By: Hoak Partners, LLC, its general partner
By: /s/ James Hoak
---------------------------------
Name: James Hoak
Title: Manager
HOAK PARTNERS, LLC
By: /s/ James Hoak
---------------------------------
Name: James Hoak
Title: Manager
/s/ James Hoak
-------------------------------------
James Hoak
/s/ Thomas Harrison
-------------------------------------
Thomas Harrison
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/s/ Frederick Pickering
-------------------------------------
Frederick Pickering
MEDIA/COMMUNICATIONS PARTNERS III LIMITED
PARTNERSHIP
By: M/C III, LLC
By: /s/ James Wade
---------------------------------
Name: James Wade
Title: Authorized Officer
MEDIA/COMMUNICATIONS INVESTORS LIMITED
PARTNERSHIP
By: /s/ James Wade
---------------------------------
Name: James Wade
Title: Authorized Officer
M/C III, LLC
By: /s/ James Wade
---------------------------------
Name: James Wade
Title: Authorized Officer
/s/ James Wade
-------------------------------------
James Wade
/s/ David Croll
-------------------------------------
David Croll
/s/ Stephen Gormly
-------------------------------------
Stephen Gormly
/s/ Christopher Gaffney
-------------------------------------
Christopher Gaffney
<PAGE>
/s/ John Hayes
-------------------------------------
John Hayes
/s/ Peter Claudy
-------------------------------------
Peter Claudy
TORONTO DOMINION INVESTMENTS, INC.
By: /s/ Martha L. Gariepy
---------------------------------
Name: Martha L. Gariepy
Title: Vice President
NORTHWOOD VENTURES LLC
By: /s/ Peter Schiff
---------------------------------
Name: Peter Schiff
Title: Authorized Person
NORTHWOOD CAPITAL PARTNERS LLC
By: /s/ Peter Schiff
---------------------------------
Name: Peter Schiff
Title: Authorized Person
/s/ Peter Schiff
-------------------------------------
Peter Schiff
/s/ Henry Wilson
-------------------------------------
Henry Wilson
<PAGE>
ONELIBERTY FUND III, L.P.
By: OneLiberty Partners III, LP,
its general partner
By: /s/ Edwin M. Kania, Jr.
------------------------------
Name: Edwin M. Kania, Jr.
Title: General Partner
ONELIBERTY FUND IV, L.P.
By: OneLiberty Partners IV, LLC,
its general partner
By: /s/ Edwin M. Kania
Name: Edwin M. Kania
------------------------------
Title: Managing Member
ONELIBERTY ADVISORS FUND IV, L.P.
By: OneLiberty Partners IV, LLC,
its general partner
By: /s/ Edwin M. Kania
------------------------------
Name: Edwin M. Kania
Title: Managing Member
ONELIBERTY PARTNERS III, LP
By: /s/ Edwin M. Kania, Jr.
------------------------------
Name: Edwin M. Kania, Jr.
Title: General Partner
ONELIBERTY PARTNERS IV, LLC
By: /s/ Edwin M. Kania
------------------------------
Name: Edwin M. Kania
Title: Managing Member
<PAGE>
/s/ Edwin M. Kania
------------------------------
Edwin M. Kania
/s/ Steve Ricci
------------------------------
Steve Ricci
WIRELESS 2000, INC.
By: /s/ Joan S. Ducote
----------------------------
Name: Joan S. Ducote
Title: President
GILDE INTERNATIONAL B.V.
By: /s/ Steve Ricci
----------------------------
Name: Steve Ricci
Title: Authorized Person
CB CAPITAL INVESTORS, LLC
By: Chase Capital Partners, its
manager
By: /s/ Michael R. Hannon
----------------------------
Name: Michael R. Hannon
Title: General Partner
<PAGE>
J.H. WHITNEY III, L.P.
By: J.H. Whitney Equity Partners III, L.L.C.,
its general partner
By: /s/ Daniel J. O'Brien
-------------------------------
Name: Daniel J. O'Brien
Title: Managing Member
WHITNEY EQUITY PARTNERS, L.P.
By: J.H. Whitney Equity Partners, L.L.C., its
general partner
By: /s/ Daniel J. O'Brien
------------------------------
Name: Daniel J. O'Brien
Title: Managing Member
WHITNEY STRATEGIC PARTNERS III, L.P.
By: J.H. Whitney Equity Partners III, L.L.C.,
its general partner
By: /s/ Daniel J. O'Brien
------------------------------
Name: Daniel J. O'Brien
Title: Managing Member
WHITNEY STRATEGIC PARTNERS III, L.P.
By: /s/ Daniel J. O'Brien
------------------------------
Name: Daniel J. O'Brien
Title: Managing Member
<PAGE>
CONSECO, INC.
By: /s/ James S. Adams
-----------------------------
Name: James S. Adams
Title: Senior Vice President, Chief
Accounting Officer and Treasurer
CIHC, INCORPORATED
By: /s/ William T. Devanney, Jr.
-----------------------------
Name: William T. Devannney, Jr.
Title: Senior Vice President,
Corporate Taxes
TRILLIUM PCS, LLC
By: /s/ William M. Mounger, II
-----------------------------
Name: William M. Mounger, II
Title: Manager
DRESDNER KLEINWORT BENSON PRIVATE EQUITY
PARTNERS LP
By: Dresdner Kleinwort Benson Private Equity
LLC, its general partner
By: /s/ Alexander P. Coleman
-----------------------------
Name: Alexander P. Coleman
Title: Authorized Person
TRIUNE PCS, LLC
By: Oak Tree, LLC, Manager
By: Triune Private Equity, LLC, Manager
By: /s/ Kevin Sheperd
-----------------------------
Name: Kevin Sheperd
Title: Co-Manager
/s/ Kevin Shepherd
------------------------------------
Kevin Shepherd
<PAGE>
J.G. FUNDING, LLC
By: Chrysalis Ventures, LLC, Manager
By: /s/ David A. Jones, Jr.
-----------------------------------
Name: David A. Jones, Jr.
Title: Manager
/s/ David Jones
-----------------------------------
David Jones
SAUNDERS CAPITAL GROUP, LLC
By: /s/ Robert S. Saunders
-----------------------------------
Name: Robert S. Saunders
Title: Manager
/s/ Robert Saunders
-----------------------------------
Robert Saunders
MON-CRE WIRELESS, INC.
By: /s/ G.L. McGee
-----------------------------------
Name: G.L. McGee
Title: General Manager
RAGLAND WIRELESS, INC.
By: /s/ Stanley Bean
-----------------------------------
Name: Stanley Bean
Title: Director
CABLEVISION SERVICES, INC.
By: /s/ Jeffrey T. Smith
-----------------------------------
Name: Jeffrey T. Smith
Title: Vice President
<PAGE>
HAYNEVILLE WIRELESS, INC.
By: /s/ Penelope Poitevint
------------------------------
Name: Penelope Poitevint
Title: President
MOUNDVILLE COMMUNICATIONS, INC.
By: /s/ Larry P. Taylor
------------------------------
Name: Larry P. Taylor
Title: President
/s/ James E. Campbell
------------------------------
JAMES E. CAMPBELL
INDIVIDUALLY AND AS BENEFICIAL OWNER OF THE
TELECORP PCS, INC. (F/K/A TELECORP-TRITEL
HOLDING COMPANY) SHARES HELD FOR MY ACCOUNT BY
SOUTH TRUST BANK, N.A. IN AN INDIVIDUAL
RETIREMENT ACCOUNT