Pretty simple really, most people that offer the service are either working for the carrier or know affiliates whom do. All they do is throw your IMEI number in a pool of unlocked approved IMEI's and just push the button. I myself used the service with my AT&T 4S and got it unlocked in less then 24hrs. When the unlock is complete they send you a e-mail saying, reconnect your device to itunes and let the factory unlock message appear. Once it does, you are all set.
