I made the switch from Sprint to T-Mobile on Monday. Was with Sprint on the $39.95 employee plan for 3 years. Using my Vogue. Waited for the release of Phone 7 on Sprint and since it wasn't coming till Feb or so, I made the switch.
GREAT Phone the HD7 and glad I made the switch. Costs me $40 more a month but I think its worth it. Just having a SIM card again to swap into different devices makes it worth it.
If your struggling like I was about making the switch, trust me; It's worth it.
Only complaint so far is the lack of BING functionality that I got so used to on my Vogue. Driving directions and movies etc. But I hear thats coming in January. Guess my Vogue will be good for something till then