Originally Posted by KnowProblem
Technically, how are they achieving that? Usually once you SIM unlock a device it is good on any carrier. Perhaps those other phones you are talking about didn't have the US GSM bands (i.e. they didn't have GSM-850 and GSM-1900), which at least according to the official Motorola specs, the photon specifically does include.
I was curious and found this: Using Sprint HTC Touch Pro 2 on At&t network - HTC Touch Pro2 (Sprint) - Windows Phone Forums - HTC Community
So it might be possible to hack the Photon in the future to work in the US GSM networks...although with the Motorola encrypted bootloader it would be a lot harder.