Thank you for reaching out. Since you are prepaid, it is standard operating procedure that data will not work while roaming. You can use any compatible phone on a prepaid account, however that will not allow data roaming,
Krystle C @ T-Force
Support Community: http://support.t-mobile.com/
Customer Care: Dial 611 or 1-800-937-8997
I am having the same problem with the exact phone HTC Inspire .... I have no idea what data roaming exactly means. I've been using a few different unlocked GSM phones before (HTC Incredible 2, LG Optimus L9, Nokia N8 etc), never happened with those phones. It rarely be able to connect to T-Mobile while I am sitting in my room.