Prospectus Supplement No. 19 Filed Pursuant to Rule 424(b)(3) (To Prospectus Dated November 2, 1999) Registration No. 333-89345 Prospectus Supplement Dated January 12, 2001 This prospectus relates to the resale by the holders of our: o $300,000,000 principal amount of 6.25% convertible notes due 2009, o $425,500,000 principal amount 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: Number of Shares Percentage of Principal Amount of Class A Common Number of Class A at Maturity of 2.25% Stock Issuable Shares of Class Common Stock Notes Beneficially Upon Conversion of A Common Stock Outstanding as Owned That May the 2.25% Notes That Beneficially of January Selling Securityholders be Sold May be Sold Owned** 11, 2001*** ----------------------- ------------------- ------------------- --------------- -------------- Goldman, Sachs & Co. (1) $1,000,000 41,666 -- ** Less than 1%. ** In addition to the shares issuable upon conversion of the notes. *** Includes shares issuable upon conversion of the notes and additional shares beneficially owned as of January 11, 2001. (1) Entity shown in the table, or an affiliate of the entity, was one of the initial purchasers of these notes and/or other notes of the Company that were sold in a private placement. The initial purchasers acquired such notes at a discount. In addition, some of these entities or their affiliates have participated in other offerings of securities by the Company and/or have performed other banking services for which they have received fees.