GSM/SIM Question

[Big Calhoun]

I think this will probably be a very rudimentary question, so I apologize now; I've never used GSM phones are carriers before. But, with the capabilities of the TP2, would I be able to use a SIM from an AT&T phone with my TP2? And would I be able to receive calls on both my numbers at the same time or would I have to alternate between the two?

I will be getting an AT&T cellphone for work so I figured I'd just take the SIM and add it to my TP2 so I could get my VzW and AT&T calls on the same device.