Happens to me at KU games in Memorial Stadium in Lawrence, KS, the Irony of course? "AT&T is the exclusive Wireless partner of the Jayhawks." Which results in multiple things on the screen asking people in the stadium to text something to AT&T. Every time "My F&*%^(NG iPhone doesn't work can be heard from throughout the stadium." Verizon, T-Mobile and Sprint work like a charm every time. It's BS really, NOTHING works, and no AT&T 3G phones work, I left the stadium and got 20 Text Messages. AT&T really needs to step up on adding capacity at stadiums, especially ones they sponsor.
(P.S the later 3 carriers have COWS set up down the street, for what seems to be permanent installations for the Football season.)