I'm new to T-Mobile, previously a long time att customer. I had lots of issues with att at home - Oklahoma City area, but found the network to be good everywhere else so put up with att for years. I can even tell you where on the highway you will lose signal on att, and areas around the airport that for some strange reason are att dead zones.
Switched to T-Mobile this summer, no issues at home at all, even in the att dead zones. I was in San Jose with a coworker who still had att. We were in the Convention Center and he couldn't make or receive calls until he went outside. On the other hand I had no issues.
I know it has been said before but T-Mobile's customer service is great. My experience was att's was at best a joke, and a bad one at that.
I know you are supposed to hate your wireless provider, but I'm very happy with my 8320 and T-Mobile. The WiFi is great, and T-Mobiles rates and service are so much better than what I used to deal with at att.