If i buy a used 3g iphone off of somebody, can i just put my sim card in it and use it. My next question is since i am a college student and dont have the money for a data plan, can i have att put a WIX block on my account before i put my sim into it. I have heard people do this but can att put the data plan back on your account if they find out. any advice would help me out a lot. I had the 1st gen iphone and sold it, big mistake.