Ironically, the technology in your model is merely a prior iteration of what's on the 4G models. In other words, it's the same technology. Your phone uses HSPA 7.2, and the 4G models use HSPA 14.4. On Verizon, this would be somewhat like the EVDO Revision 0 (3G) versus EVDO Revision A (3G), with less of a speed difference. Also, someone would probably take this moment to point out that what T-Mobile calls 4G today, they called 3G not too long ago.

With T-Mobile, as I understand it, you're essentially linking into a "4G" tower, but getting "3G" speeds. Moving to one of T-Mobile's 4G models should give you the exact same connection, only with faster data speeds.

My personal experience with T-Mobile isn't that great. My wife was on T-Mo before I married her, and it was one headache after another for us. And she was on a basic flip phone, which you would expect to be a tried and true experience.