SIM card transfers?

[Traxan]

I'm embarrassed my Google Fu failed me on such a basic question, so go easy on me please.

I have a iPhone 4, the old man has a 3GS and bitches endlessly about the power drain. If I upgrade to a 4S, can I take his SIM card from the 3GS and put it in my old 4? No jailbreaking, just transferring SIM cards.

 

[eekcat]

the 4/4S uses a microSIM, so you'll either need a SIM cutter, or to just get a new microSIM from AT&T and ask them to move his service to the new one.

 

[takeshi74]

^ This and if both of you are on the same carrier since you don't mention whether it's unlocked or not. JB isn't relevant.