My E900 is Orange France and C900 is AT&T.
From my understanding I can go buy unlock codes from diverse vendors to unlock the phone. But when I insert my SIM card(non ORG, non AT&T) the device never asks me to input any codes. Instead it just tells me the device is missing SIM or SIM is invalid.
Is there any code that prompts to change SIM code?
Also, what's the difference between debranding and buying a SIM code?