You're thinking of T9, which is for typing text. When you dial 800-AAAAAAA, you're not typing, you're dialing. The "A" character is just on the same button as t

You're thinking of T9, which is for typing text. When you dial 800-AAAAAAA, you're not typing, you're dialing. The "A" character is just on the same button as the "2". So when you press "A" seven times you're really pressing "2" seven times. You end up dialing 800-2222222. There's nothing funny happening, "A" is just another symbol printed on the "2" button.