krnfrk6663 -- you are welcome to come along.
Hopefully, we'll find out what we need to do to be able use SIM cards other than the "roaming" card that Sprint might provide like they did with the TP2.
I think enabling the Photon to use SIM cards from overseas carriers when overseas should be easy to get Sprint to do (like with the TP2) , if its not automatic. However, I don't know know if the GSM radio is "unlocked" for use with SIM cards from the US domestic GSM carriers (AT&T and T-Mobile, etc.), or if it is even doable. It took the efforts of a couple of the super chefs to "unlock" the TP2's GSM radio so it would work with SIM cards from the domestic GSM carriers.
Hopefully, we'll get some answers soon.