3GS that should be factory unlocked, but is not
a friend recently bought iPhone 3GS 16GB which seller said is factory unlocked version from Hong Kong. When I go to Settings it shows Model number MB131ZP which means it's exactly that version.
However, I've had no luck getting it to work with his SIM card. It recognizes the SIM, asks for a PIN, but then shows just one bar and no carrier. I've tried restarting, turning airplane mode, but with no result other than "SIM Failure" popup.
What's could be wrong?
Is it possible that it's just some temporary error that will be resolved by restoring or updating the phone (it's currently on 4.0.1)?
Is it possible that it's a scam? That it's AT&T-locked version and model number was somehow modified? (therefore by updating to 4.1, he'll lose all chances for getting it to work). Is it possible to modify the Model number and if yes, is it possible to discover "true" country of origin (or if it's factory locked or unlocked)?
Thanks for any help and suggestions.