I've had both in my 900, in the Balt/DC corridor. "Coverage area" is about the same, but the problem I have with T-Mo is the weak building penetration for "some" buildings. I don't remember what being on Edge was like w/AT&T...signal "loss" was not an issue, but signal strength fluctuation was evident, even when just moving the phone a few inches, of maybe a bar or two. I think its just the nature of 2G, much like Verizon's CDMA/1x.

My phone pretty much stays on "full bars" with T-Mo. However I'll be switching back to AT&T, and most likely another phone (CNBC now has real-time stock quotes for pre-market, and Sling is coming out in summer, for Android) just because of the building issue. Being on call 24/7 won't allow for being in dead zones in otherwise "full bar" areas.

I will miss those great T-Mo no contract rates and 7Mb speeds though.