Well what would happen if you had 2 iPhones? One is active and one not active without the sim card. Could you take the active sim and put it in the non-active and update, then switch the sim back to the active?
off-hand, I would say no, but obviously if you have an unlocked phone on
T- Mobile and you can sync, I would expect that you should be able to swap around SIM cards.
But the reason I say no is because an iPhone SIM will work in Any GSM phone, Not any SIM can work in the iPhone - even if it's an AT&T SIM. So I would suspect that the SIMs are IEMI encoded when registered, and that keeps the chip from activating other iPhones.