Can you switch the iPhone 4 SIM card with an iPhone 4S SIM card?

My mom has an iPhone 4S for sprint and I have an iPhone 4 for AT&T. Is it possible to switch SIM cards?

That will not be possible since both carriers run on different networks.AT&T runs on GSM network, which uses sim cards, but Sprint is on a CDMA network, which does not use sim cards, despite all 4Ss having the sim tray.