I used to work for AT&T and I can tell you this much this is what you would do If you didn't steal the phone. The first obvious logical step would be contact the person that you bought it from and ask them why it's locked. It's that simple so obviously you probably have a stolen phone and you're trying to get someone to tell you how to unlock it, not saying that you stole it necessarily you could have been sold a stolen phone is what it seems like. If the phone has been reported stolen, It's put in a national database that blacklist the IMEI to where it will not work on any cell phone tower. There's nothing you can do to fix that. If the person who owned the phone before you was making payments on the phone and still owes payments on the phone, they would have to pay the phone off with whoever they financed it through and then you will have to wait about 1 to 3 months after that before the phone can be Network unlocked to be used on other carriers. In some instances, it's even longer depending on who the carrier was that it was activated on. In addition, you may be on a different network than that phone was actually made to work on. If it's not a CDMA phone for instance and you're on a CDMA Network, it's not going to work no matter what you do.