I've used Cingular (AT&T) since about 2001 now. I've stuck with them because I've always been pleased with the coverage and reception, and the few times I've had to deal with customer service, they were pleasant enough.

I've noticed a slip in service lately though. It's ironic that they advertise the lowest rate of dropped calls, because sometimes you flat out can't call. Probably once a week (sometimes more, sometimes less) I'll get a "service not available" message when trying to dial. If I try again immediately, the call usually goes through, but it is somewhat annoying.

There are the usual pockets of bad receptivity, but you'll find that anywhere you go. Generally speaking, coverage is pretty widespread and good.

There has been one glitch that I've run into since getting my new phone in May. I don't know if it's related specifically to my phone model (LG CU500v) or something all AT&T customers may deal with (or if it's something related to upgrading my number from the old network to the new one - but that shouldn't have anything to do with it). But, sometimes my phone will not make the switch to a new tower. This happens more often when I travel (it happened to me at Tcon, actually...). So far it has only happened three times, I think. I now know that turning the phone off and back on is a quick fix, but it is a frustrating glitch (especially when you don't know what's happening).

So, other than those few problems, I've been pretty happy with Cingular and still am.