FWIW, I had the same issue when I was trying to use a prepaid T-Mobile SIM on my unlocked Sprint TP2. Evenything worked but Internet. I initially thought the issue was with the radio (like the previous poster said) or a bad setting. But when I plugged my friends T-Mobile SIM in my phone (he had a monthly plan + data) Internet & data worked like a charm. Try that first before mucking around with any settings.
BTW, this worked on the 2.32WU radio.