hi a bought a iphone 3gs off a freind today its not letting me do anything i have restored all settings back to factory settings but wont let me activate iphone

What error do you receive when trying to activate?

Are you using the same Carrier as your friend, or a different one?

If different Carrier, are you certain the iPhone is unlocked? A locked device will of course prevent you from using SIM cards not from the Original Carrier that the device was locked too.