I bought a Samsung Galaxy S3 from craigslist (I know, Bad Idea). Ive tried to activate the phone through straight talk but they say its an invalid IMEI# and that its inactive. Ive also tried buying a Straight talk SIM card and installing that, still no service. Idk what to do, is there something someone could have done to the phone ie Flashing or unlocking that would change the IMEI from a straight talk phone to another? Please HELP! Thanks in advance for any advice.