AT&T INC. U.S.$5,000,000,000 U.S.$1,150,000,000 4.550% GLOBAL NOTES DUE 2032 U.S.$1,250,000,000 4.900% GLOBAL NOTES DUE 2035 U.S.$1,100,000,000 5.550% GLOBAL NOTES DUE 2045 U.S.$1,500,000,000 5.700% GLOBAL NOTES DUE 2054 UNDERWRITING AGREEMENT