We're excited that the iPad's data plans won't lock you down in a 2-year contract and that the device's 3G modem isn't carrier-locked. But you still won't get 3G speeds on an iPad if you decide to use T-Mobile.
Why? The iPad's 3G modem supports UMTS/HSDPA (850, 1900, 2100 MHz) and GSM/EDGE (850, 900,1800, 1900 MHz). T-Mobile's 3G runs on 1700 Mhz. See the trouble? You could of course still get EDGE data service using T-Mobile, but that's just not as great as the theoretically blazing 3G speeds, is it?
Some of you are remarking that T-Mobile also runs on 2100 MHz, but here's what our friend and wise man Richard Baguley says:
UMTS2100 is the european version, not the US one. I don't think they are compatible. So, the iPad would just not see the T-Mobile 3G on either frequency