Folks,Cingular customer service is a crap shoot and all depends on the call center handling you and which 'legacy' carrier it was a part of. Folks on the Cingular 'Blue' network (former AT&T), I feel for you. You're going to have HORRID Customer Service until they clean AT&T up which is taking forever. The folks you talk to will be nice but they won't be able to do much to help and won't know much about what's going on.
Former SNET customers in CT? Not a clue what service is like. Same for Comcast customers. Former Bellsouth areas (FL, GA, SC, LA) should be decent for customer service and SBC areas will have good customer service (TX, OK, AR, KS, IL)... unsure about CA and the west, no experience. But, yes, until Cingular fully knits everything together and applies uniform standards you're looking at some differences depending on where you live if you go Cingular.
For my part, Cingular customer service is lightyears beyond Sprint, T-Mobile, or anyone else for that matter. I have had great luck with 'em and if I get someone unhelpful, I ask for a supervisor who addresses the problem.