Can a Sprint iPhone be tracked down?

Alright, so my friend found an iPhone (4 or 4S not really sure) recently at a local park on a bench. Seems kind of weird right? Well anyways, he said it has a password and he wants to keep the phone (I don't want to hear that "Return it & be nice") because he obviously wants to keep the iPhone. I mean who doesn't? Anyways he checked the top and it said Sprint. So immediately he took out the SIM card & turned off the phone. Is there anyway the phone can still be traced? If so how? & What are the steps to not getting it traced?