It's not stolen. It's completelly legal. But I've heard that there are two IMEI. One in the OTP (which you find on the back of the phone) and one in the GDFS. If both IMEI don't match each other, the phone is dead. As I said I don't think that I've done anything to the IMEI but I want to be sure before I send it to a service center because it's illegal to change the IMEI