After being on ATT for 7 years, my bill started fluctuating wildly from $60 to $100 even though I wasn't doing anything different from previous billing periods.
After I called ATT and sat on the phone with them for two hours, a representative told me they were "singling out my blackberry plan" and could do nothing about the issue. I gave up, walked into T-mobile while I still had an ATT rep on the phone and let them know I was going to get more minutes and a cheaper plan.
This was three days ago and i think I'm going to call ATT and waste some more of their time while officially closing my account.
On a similar note, my roommates all have ATT and hate their coverage and service. Another friend goes so far as to call her phone an imnotaPhone. ATT service is so bad, they have a piece of software that allows customers to help map out and complain about where the service is bad. They also claim that an 80% success rate on connecting calls is good. Cricket, AllTell, T-Mobile, MetroPCS, smokesignals, homing pidgeons, and morse code all beat ATT. Do yourself a favor, go with anyone but ATT.