We used Cingular and never had any issues with them. AT&T bought Cingular and we had problem after problem with them. Constant billing issues, false charges, etc. We had to call them every month to clean something up. Hated their customer service too.
We finally said the hell with it and paid the fee to get out of our contract. We switched to T-Mobile as they had much better rates and we went to a no contract plan. We have had pretty good luck with T-Mobile. The coverage can be a bit spotty and you will drop you call a few blocks from our house coming in from the West. The price is good and we like the unlimited text and web. A lot of people my wife talks to are on T-Mobile so we get to talk to them for free. So far we have had no issues with custom service either, they have always been very helpful.
Now AT&T comes along and will probably screw this all up again. I am not looking forward to the buy out at all. I cringe at what will happen to our billing. I am sure the rates will go up. I hope we get better coverage and less dropped calls but I am sure there will be so much more pain.