I travel very extensively and T-Mobile really works for me. I have used both AT&T and T-Mobile very heavily over the last 6 years. I find AT&T and T-Mobile coverage about the same in most areas. If you stay in cities, metro areas, interstates, major highways you really won't have any issues.

T-Mobile has way superior customer service. AT&T is ok until you have to call customer service. T-Mobile customer service is awesome


T-Mobile voice international roaming is much cheaper then AT&T in most places.

T-Mobile data roaming is cheaper (I think as well). With Blackberry you can pay an additional $20 flat fee and get unlimited international data roaming. I add this option before I go International and discontinue it when I come back stateside.

T-Mobile has given me unlocked codes any phone I have ever owned with them. AT&T is a real pain about this so it's hard to use other SIMs when you travel.

No Blackberries have 3G so the AT&T and T-Mobile both only do EDGE. More then sufficient for email and the occasional web browsing on the phone itself.

The Blackberry Cruve on T-Mobile has Hotspot@Home which means you can pay $20 (or $10 if your lucky) and get unlimited calls whenever you have a wifi connection on the phone over the Internet. T-Mobile has profiles which basically let you get free calls on the phone whenever you are in a T-Mobile hotspot. So when I am at home, Starbucks, airport, or wherever I have a wifi Internet connection or in a T-Mobile hotspot I get unlimited calls for free. You don't have to have an additional T-Mobile Hotspot service; the phone recognizes automatically it is on a T-Mobile hotspot (or any wireless network you setup) and starts making calls over wifi for free (when you pay the extra $10 - $20 for the Hotspot@Home service).