I've got an iPhone 4S which is locked to the O2 network in the UK. Looking on their website they sat they unlock contract iPhones for free. It does state to have the mobile number you purchased the phone with but not sure if it'd work with me as I didn't get that 4s when I renewed my contract? I have an O2 contract, but the 4s was bought secondhand from the Preowned section at a Game store. Can I still get this iPhone unlocked for free, or will it cost me as I'm not the original owner?