For most iPhone owners, it seems like AT&T is deaf to our complaints about signal quality. It appears, however, that griping loudly and repeatedly to the company does have an effect.
I live in the suburbs south of Denver and my signal quality is pretty good. However, whenever my wife and I have gone to Colorado Rockies baseball games in the last few years (we're season ticket holders), we've had awful service at the ballpark. Although the signal strength indicator would show five bars, it was impossible to do much of anything with our iPhones or iPads. Even trying to send out text messages would fail, and attempts to use the MLB At-Bat app in the ballpark were laughable to the point that I didn't purchase the app for the 2010 season. What was even more frustrating is that AT&T is a ballpark advertiser at Coors Field, so you think they'd want their service to be excellent.