It used to be that if you wanted your iphone unlocked (this may still be true) you had to beg your carrier to do it. THey would submit a ticket to their internal team, and within 48 hours your phone would get the go ahead to unlock itself. Even if you had bought the phone, or fulfilled your contract, the carriers in the US would frequently refuse to unlock. The workaround was to go to some sketchy guy in a strip mall, give them $50, then they would somehow get someone at the carrier to unlock the phone. I suspect this guy had something to do with it.

Carrier-locked phones are a real stupid idea that should have been legislated away a long time ago