Okay, even though the plan says "Unlimited 4G only on TMobile network" or something along those lines my iPhone 4 is able to get 3G in areas.
It's amazingly fast and a change from edge. I get about 6mbps download speed. In about a day I used over 2GB and TMobile hasn't said a thing yet.
Before that I had the 2GB plan for $10 that throttles, also worked with 3G then throttled to slower than edge lol.