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                                                                     Exhibit 4.4

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                       CROWN CASTLE INTERNATIONAL CORP.

                                   As Issuer

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                             SERIES A AND SERIES B

                                 $251,000,000

                    10 5/8% Senior Discount Notes due 2007

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                            SUPPLEMENTAL INDENTURE

                         Dated as of December 20, 1999

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Supplementing the Indenture dated as of November 25, 1997, between Crown Castle
International Corp., as Issuer, and United States Trust Company of New York, as
                                    Trustee

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                    UNITED STATES TRUST COMPANY OF NEW YORK

                                  As Trustee

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   SUPPLEMENTAL INDENTURE dated as of December 20, 1999, between Crown Castle
International Corp., a Delaware corporation (the "Company"), and United States
Trust Company of New York (the "Trustee"), as Trustee under the Indenture
referred to herein.

   WHEREAS the Company and the Trustee heretofore executed and delivered an
Indenture dated as of November 25, 1997 (the "Indenture"), in respect of the
Company's $251 million aggregate principal amount of 10 5/8% Series A Senior
Discount Notes due 2007 and 10 5/8% Series B Senior Discount Notes due 2007
(collectively, the "Securities");

   WHEREAS Section 9.02 of the Indenture provides that the Company and the
Trustee may amend the Indenture with the consent of the Holders of at least a
majority in aggregate principal amount of the Securities then outstanding;

   WHEREAS the Company desires to amend certain provisions of the Indenture, as
set forth in Article I hereof;

   WHEREAS the Holders of a majority in aggregate principal amount of the
Securities outstanding have consented to the amendments effected by this
Supplemental Indenture; and

   WHEREAS this Supplemental Indenture has been duly authorized by all
necessary corporate action on the part of the Company.

   NOW, THEREFORE, the Company and the Trustee agree as follows for the equal
and ratable benefit of the Holders of the Securities:

                                   ARTICLE I

                                  Amendments

   SECTION 1.01.  Amendment to Section 4.07.  The first full paragraph
following clause (c) of Section 4.07 (Restricted Payments) of the Indenture is
hereby deleted in its entirety and replaced with the following:

      "The foregoing provisions shall not prohibit (i) the payment of any
   dividend within 60 days after the date of declaration thereof, if at said
   date of declaration such payment would have complied with the provisions of
   this Indenture; (ii) the making of any Investment or the redemption,
   repurchase, retirement, defeasance or other acquisition of any subordinated
   Indebtedness or Equity Interests of the Company in exchange for, or out of
   the net cash proceeds of the substantially concurrent sale (or, in the case
   of an Investment, a sale within the previous 12 months) (other than to a
   Subsidiary of the Company) of, any Equity Interests of the Company (other
   than any Disqualified Stock); provided that such net cash proceeds are not
   used to incur new Indebtedness pursuant to clause (x) in Section 4.09; and
   provided further that, in each such case, the amount of any such net cash
   proceeds that are so utilized shall be excluded from clause (c)(ii) of the
   preceding paragraph; (iii) the defeasance, redemption, repurchase or other
   acquisition of subordinated Indebtedness with the net cash proceeds from an
   incurrence of Permitted Refinancing Indebtedness; (iv) the designation of
   CTSH as an Unrestricted Subsidiary immediately following the Roll-Up; or (v)
   the payment of any dividend by a Restricted Subsidiary of the Company to the
   holders of its Equity Interests on a pro rata basis.".

   SECTION 1.02.  Amendments to Section 4.09. (a) Modification of the Leverage
Test.  The first paragraph of Section 4.09 (Incurrence of Indebtedness and
Issuance of Preferred Stock) of the Indenture is hereby deleted in its entirety
and replaced with the following:

      "The Company shall not, and shall not permit any of its Restricted
   Subsidiaries to, directly or indirectly, create, incur, issue, assume,
   guarantee or otherwise become directly or indirectly liable, contingently or
   otherwise, with respect to (collectively, "incur") any Indebtedness
   (including Acquired

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   Debt) and the Company will not issue any Disqualified Stock and will not
   permit any of its Restricted Subsidiaries to issue any shares of preferred
   stock; provided that the Company may incur Indebtedness (including Acquired
   Debt) or issue shares of Disqualified Stock and the Company's Restricted
   Subsidiaries may incur Indebtedness (including Acquired Debt) or issue
   preferred stock if, in each case, (i) no default shall have occurred and be
   continuing or would result as a consequence thereof and (ii) the Company's
   Debt to Adjusted Consolidated Cash Flow Ratio at the time of incurrence of
   such Indebtedness or the issuance of such Disqualified Stock or preferred
   stock, after giving pro forma effect to such incurrence or issuance as of
   such date and to the use of proceeds from such incurrence or issuance as if
   the same had occurred at the beginning of the most recently ended four full
   fiscal quarter period of the Company for which internal financial statements
   are available, would have been no greater than 7.5 to 1.".

   (b) Modifications to the "Permitted Debt" Definition. (i) Modification of
Formula for Credit Facilities Indebtedness.  The first clause of the definition
of "Permitted Debt" contained in Section 4.09 (Incurrence of Indebtedness and
Issuance of Preferred Stock) of the Indenture is hereby deleted in its entirety
and replaced with the following:

      "(i) the incurrence by the Company or any of its Restricted Subsidiaries
   of Indebtedness under Credit Facilities in an aggregate principal amount
   (with letters of credit being deemed to have a principal amount equal to the
   maximum potential liability of the Company and its Restricted Subsidiaries
   thereunder) at any one time outstanding not to exceed (x) in the case of an
   incurrence on or before December 31, 2000, the greater of (I) $500.0 million
   or (II) an amount equal to the Adjusted Consolidated Cash Flow of the
   Company at the time of such incurrence multiplied by 8; (y) in the case of
   an incurrence during the period beginning on and including January 1, 2001
   to and including December 31, 2001, an amount equal to the Adjusted
   Consolidated Cash Flow of the Company at the time of such incurrence
   multiplied by 7.5; and (z) in the case of an incurrence after December 31,
   2001, an amount equal to the Adjusted Consolidated Cash Flow of the Company
   at the time of such incurrence multiplied by 6.5;".

      (ii) Modification of Acquired Debt Basket.  The ninth clause of the
   definition of "Permitted Debt" contained in Section 4.09 (Incurrence of
   Indebtedness and Issuance of Preferred Stock) of the Indenture is hereby
   deleted in its entirety and replaced with the following:

          "(ix) the incurrence by the Company or any of its Restricted
       Subsidiaries of Acquired Debt in connection with the acquisition of
       assets or a new Subsidiary and the incurrence by the Company's
       Restricted Subsidiaries of Indebtedness as a result of the designation
       of an Unrestricted Subsidiary as a Restricted Subsidiary; provided that,
       in the case of any such incurrence of Acquired Debt, such Acquired Debt
       was incurred by the prior owner of such assets or such Restricted
       Subsidiary prior to such acquisition by the Company or one of its
       Restricted Subsidiaries and was not incurred in connection with, or in
       contemplation of, the acquisition by the Company or one of its
       Restricted Subsidiaries; and provided further that, in the case of any
       incurrence pursuant to this clause (ix), as a result of such acquisition
       by the Company or one of its Restricted Subsidiaries, the Company's Debt
       to Adjusted Consolidated Cash Flow Ratio at the time of incurrence of
       such Acquired Debt, after giving pro forma effect to such incurrence as
       if the same had occurred at the beginning of the most recently ended
       four full fiscal quarter period of the Company for which internal
       financial statements are available, would have been less than the
       Company's Debt to Adjusted Consolidated Cash Flow Ratio for the same
       period without giving pro forma effect to such incurrence;".

   SECTION 1.03.  Amendment to Section 4.17.  The following sentence is hereby
added to the end of Section 4.17 (Limitation on Issuances and Sales of Capital
Stock of Restricted Subsidiaries) of the Indenture:

      "Notwithstanding the foregoing, the issuance or sale of shares of Capital
   Stock of any Restricted Subsidiary of the Company will not violate the
   provisions of the immediately preceding sentence if such shares are issued
   or sold in connection with (x) the formation or capitalization of a
   Restricted Subsidiary or (y) a single transaction or a series of
   substantially contemporaneous transactions whereby such Restricted
   Subsidiary becomes a Restricted Subsidiary of the Company by reason of the
   acquisition of securities or assets from another Person.".

   SECTION 1.04.  Trustee's Acceptance.  The Trustee hereby accepts this
Supplemental Indenture and agrees to perform the same under the terms and
conditions set forth in the Indenture.

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                                  ARTICLE II

                                 Miscellaneous

   SECTION 2.01.  Interpretation.  Upon execution and delivery of this
Supplemental Indenture, the Indenture shall be modified and amended in
accordance with this Supplemental Indenture, and all the terms and conditions
of both shall be read together as though they constitute one instrument, except
that, in case of conflict, the provisions of this Supplemental Indenture will
control. The Indenture, as modified and amended by this Supplemental Indenture,
is hereby ratified and confirmed in all respects and shall bind every Holder of
Securities. In case of conflict between the terms and conditions contained in
the Securities and those contained in the Indenture, as modified and amended by
this Supplemental Indenture, the provisions of the Indenture, as modified and
amended by this Supplemental Indenture, shall control.

   SECTION 2.02.  Conflict with Trust Indenture Act.  If any provision of this
Supplemental Indenture limits, qualifies or conflicts with any provision of the
TIA that is required under the TIA to be part of and govern any provision of
this Supplemental Indenture, the provision of the TIA shall control. If any
provision of this Supplemental Indenture modifies or excludes any provision of
the TIA that may be so modified or excluded, the provision of the TIA shall be
deemed to apply to the Indenture as so modified or to be excluded by this
Supplemental Indenture, as the case may be.

   SECTION 2.03.  Severability.  In case any provision in this Supplemental
Indenture shall be invalid, illegal or unenforceable, the validity, legality
and enforceability of the remaining provisions shall not in any way be affected
or impaired thereby.

   SECTION 2.04.  Terms Defined in the Indenture.  All capitalized terms not
otherwise defined herein shall have the meanings ascribed to them in the
Indenture.

   SECTION 2.05.  Headings.  The Article and Section headings of this
Supplemental Indenture have been inserted for convenience of reference only,
are not to be considered a part of this Supplemental Indenture and shall in no
way modify or restrict any of the terms or provisions hereof.

   SECTION 2.06.  Benefits of Supplemental Indenture, etc.  Nothing in this
Supplemental Indenture or the Securities, express or implied, shall give to any
Person, other than the parties hereto and thereto and their successors
hereunder and thereunder and the Holders of the Securities, any benefit of any
legal or equitable right, remedy or claim under the Indenture, this
Supplemental Indenture or the Securities.

   SECTION 2.07.  Successors.  All agreements of the Company in this
Supplemental Indenture shall bind its successors. All agreements of the Trustee
in this Supplemental Indenture shall bind its successors.

   SECTION 2.08.  Trustee Not Responsible for Recitals.  The recitals contained
herein shall be taken as the statements of the Company and the Trustee assumes
no responsibility for their correctness.

   SECTION 2.09.  Certain Duties and Responsibilities of the Trustee.  In
entering into this Supplemental Indenture, the Trustee shall be entitled to the
benefit of every provision of the Indenture relating to the conduct or
affecting the liability or affording protection to the Trustee, whether or not
elsewhere herein so provided.

   SECTION 2.10.  Governing Law.  This Supplemental Indenture shall be governed
by, and construed in accordance with, the laws of the State of New York but
without giving effect to applicable principles of conflicts of law to the
extent that the application of the laws of another jurisdiction would be
required thereby.

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   SECTION 2.11.  Counterpart Originals.  The parties may sign any number of
copies of this Supplemental Indenture. Each signed copy shall be an original,
but all of them together represent the same agreement.

   IN WITNESS WHEREOF, each party hereto has caused this Supplemental Indenture
to be signed by its officer thereunto duly authorized as of the date first
written above.

                                              CROWN CASTLE INTERNATIONAL CORP.,

                                              by  -----------------------------
                                                  Name: W. Benjamin Moreland
                                                  Title: Senior Vice President
                                                    and Treasurer

                                              UNITED STATES TRUST COMPANY OF
                                                NEW YORK, as Trustee,

                                              by  -----------------------------
                                                  Name:
                                                  Title: