iphone 3 very old device

now i hav recently got an iphone 3 and was able to use it briefly to make sure i was able to use it since it was in a pawn shop but since it has no sim car an i dont have the funds to get one anyways since i would really only be using it on wifi. i wanted to sign into my account so i did a complete reset and now it wants a sim card to activate it but i dont need it activated i just want to use it immediately on wifi i dont need a phone plan any way around this also using itunes on laptop requests same thing to insert sim to use. please help.