Prospectus Supplement No. 2                    Filed Pursuant to Rule 424(b)(3)
(To Prospectus Dated November 2, 1999)         Registration No. 333-89345


                              Prospectus Supplement
                             Dated December 2, 1999


This prospectus relates to the resale by the holder of our:

o        $300,000,000 principal amount of 6.25% convertible notes due 2009,

o        $425,500,000  principal amount at maturity of 2.25%  convertible  notes
         due 2009, and

o        the shares of Class A common  stock  issuable  upon  conversion  of the
         notes.

         This prospectus  supplement should be read in conjunction with, and may
not be delivered or utilized  without,  the  prospectus  dated November 2, 1999,
including any amendments or supplements  thereto. The terms of the notes are set
forth in the prospectus.

         The  information  in the table  appearing  under the  heading  "Selling
Securityholders"  on page 42 in the  prospectus is hereby  amended by adding the
information below with respect to selling  securityholders not previously listed
in  the  prospectus  or  in  any  amendments  or  supplements  thereto,  and  by
superceding the information with respect to selling  securityholders  previously
listed in the prospectus or in any  amendments or  supplements  thereto that are
listed below:


                                               Principal      Percentage      Number of Shares
                                               Amount at       of 6.25%          of Class A                    Percentage of
                                              Maturity of        Notes          Common Stock      Number of    Class A Common
                                              6.25% Notes     Outstanding      Issuable Upon      Shares of         Stock
                                              Beneficially       as of       Conversion of the     Class A     Outstanding as
                                               Owned That     December 1,     6.25% Notes That     Common      of December 1,
       Selling Securityholders                May Be Sold        1999            May Be Sold     Stock Owned       1999**
       -----------------------                -----------     ----------     -----------------   -----------   --------------
                                                                                                     
Allstate Insurance Company                     $ 3,750,000       1.41             153,688              --            *
Associated Electric & Gas Insurance Services   $ 1,000,000        *                40,983              --            *
Limited
BNP Arbitrage SNC                              $ 4,500,000       1.69             184,426              --            *
Continental Assurance Company                  $ 5,600,000       2.10             229,508              --            *
Global Bermuda Limited Partnership             $ 1,000,000        *                40,983              --            *
Lakeshore International, Ltd                   $ 2,000,000        *                81,967              --            *
Putnam Convertible Income-Growth Trust         $ 3,000,000       1.12             122,950              --            *
Tribeca Investments LLC                        $ 6,500,000       2.44             266,393              --            *
                                               ===========      =====           =========          ========       ======
TOTAL                                          $27,350,000      10.25           1,120,898               0            *


                                               Principal      Percentage      Number of Shares
                                               Amount at       of 2.25%          of Class A                    Percentage of
                                              Maturity of        Notes          Common Stock      Number of    Class A Common
                                              2.25% Notes     Outstanding      Issuable Upon      Shares of         Stock
                                              Beneficially       as of       Conversion of the     Class A     Outstanding as
                                               Owned That     December 1,     2.25% Notes That     Common      of December 1,
       Selling Securityholders                May Be Sold        1999            May Be Sold     Stock Owned       1999**
       -----------------------                -----------     ----------     -----------------   -----------   --------------
                                                                                                     
J.P. Morgan Securities Inc.                    $ 5,000,000       1.38             208,333              --            *
The TCW Group, Inc.                            $67,015,000      18.48           2,792,291              --          1.90
                                               ===========      =====           =========          ========       ======
TOTAL                                          $72,015,000      19.86           3,000,624              0           2.03


*   Less than 1%.

** Includes shares issuable upon conversion of the notes and shares beneficially owned as of December 2, 1999.