AT&T INC. U.S.$3,500,000,000 U.S.$1,000,000,000 4.700% GLOBAL NOTES DUE 2030 U.S.$1,250,000,000 5.375% GLOBAL NOTES DUE 2035 U.S.$1,250,000,000 6.050% GLOBAL NOTES DUE 2056 UNDERWRITING AGREEMENT