Don't have TMobile but recently bought a Verizon Hot Spot off ebay. It is a Verizon Jetpack that has been reflashed for 3G service. $5 bucks a month unlimited data. Not contract. We are extremely happy. For surfing the web, email or RV.net 3G is fine. In fact we are sitting in the 5er at the campground using it now.
Here is a link to the thread I found out about it from.
Good luck, John