AT&T is marginal at best. Their data signal is ALWAYS slower (even in the middle of town), even if you don't have trouble making regular phone calls. You also won't be able to send texts, emails or make calls on game day if you're anywhere near Kyle Field or campus in general, but you can still use your iPhone to weigh down the napkins when the wind picks up near your tailgate spot, so its not necessary to leave it at the house or anything.
Verizon has excellent coverage throughout the region. They have more repeaters and access points, primarily because of the numerous state and federal contracts they have to provide uninterrupted communication. Also, (and maybe more importantly) I can send a text message and call out during Aggie Football games from inside Kyle Field.