[Bigsmith]

Yes, you can use China Mobile etc. sims overseas. The Sprint TP2 is unlocked out of the box for any sim when used outside of the U.S. This has been confirmed. It will NOT work on U.S. GSM networks (at least not yet, eventually someone may hack this).

There is a phone setting for CDMA/GSM which you need to switch over to either "global" or "GSM" in order to use a GSM SIM overseas. But regardless how you set this your T-Mobile sim won't work, since you're in the U.S.