I've got an AT&T tilt here right next to my Sprint Touch Pro. Couple of interesting things for those who are not in the GSM/SIM know...
* better battery life - GSM sucks less gas
* simultaneous voice and 3g data
* SIM SIM SIM (if you ever get off this rock to yonder shores, you'll be happy tossing in a local pay-as-you-go sim card.)
* rollover minutes. If you can, get that low minute plan and then let em pile up
For me the at&t phone is a work prototype plan, data use mostly. I think I have something like 10K rollover minutes by now
And yes, AT&T sucks too. Just differently. Good luck over there...er, over here!