I've got AT&T (I voted cingular, for obvious reasons). I wouldn't change my Cell Phone Provider for anything, they have the best customer support, plus crazy sweet plans.
I have AT&T(formally known as Cingular) and I live in a mountainous area. The service here bites. I get service in the towns but in the mountains, zilch! Just got a new phone last week. hehe the Samsung Blackjack and I love it!
Not so bad. My bill is usually around 120$ thats w/ unlimited text and internet use plus my minutes and features.