Calling Cingular (now ATT) customer service is like calling the cable company. You are on hold for 30 or more minutes only to then be transferred repeatedly and disconnected. I switched to TMobile 6 months ago and the difference is like night and day. TMobile is also saving me 20% over Cingular ATT particularly with their "My Faves" program. I will never go back to Cingular ATT.
I agree that TMobile is a better value than Cingular. Cingular at the moment has better international data packages than TMobile. I wish Tmobile would copy them, or better yet, adopt the roaming packages they are currently rolling out in Europe.