I have AT&T. They're fine out here in the suburbs, but in Chicago, they suck ass. I can't use my iphone in my office building unless I'm in an exterior office. Since I have an interior office, that kind of sucks. Last time I was in St. Louis, I couldn't get my old iphone to work downtown at all, even OUTSIDE. I was bitching about it while some lady was walking past me, and she said "You must have AT&T." I guess when they draped that orange thing over the Arch, it blocked the signal.
Friday night my wife and I were out and started chatting with a lady who is a customer service rep for AT&T. I asked her about the cellular problem, and she said that since AT&T has so many more customers than any other provider, their network is overloaded in urban areas, but they're working on it. No timeframe, though.
Of course, this doesn't stop them from taking my money in the meantime.
I have AT&T for home internet and home phone, and all the alternative providers suck just as bad or worse, so I'm stuck with them. IMO, all of these companies have wretched customer service and charge too much. Just pick your poison and deal with it, I guess. Either that or yell out the window.