I've been lucky enough to get some free tix to several Bears games the last few years, and have taken/used an iPhone 3G, 3GS, and this year an iP4 at Soldier Field. Every single time while watching the game the signal was garbage.
There's a short window at the very beginning of halftime where data works. Otherwise, forget it.
What was worse was seeing U2 at Soldier Field. There wasn't even an intermittent signal. For the entire night.
As a general rule, any time you're in a big city and/or near/around tall buildings, getting any kind of consistent data connection is a crapshoot. Same was true when I was with Verizon and went downtown (Chicago); signal reliability was either non-existent or spotty at best...never consistent.