Expanding on what Brandon said, there are no third-party services that can legitimately unlock a phone. Any third-party service is doing one of the following:
- hacking your iPhone to unlock it. It will relock the next time you update or restore iOS.
- working with someone inside the cell carrer that they pay to without authorization enter in your phone into the carrier's unlock database. The carriers generally find out about this quickly and will relock your phone and may cancel your service.
- following exactly the same procedure you would with the carrier, but charge you for the service in addition to any carrier charges.
As Brandon said, only the carrier to whom the iPhone is locked can authorize unlocking. If they charge to do so, then you'll just have to pay it if you want your iPhone officially and permanently unlocked.
Regards.