The switch can be activated by any phone (cell or otherwise) as long as it recognizes the number. You can program several numbers into the unit. As to using different carriers for the unit's simcard you would have to ask Aerotherm but I think so as long as you have the ability (phone that accepts the simcard) to set it up correctly. As I noted in the comments the switch is available stand alone from other sources.
Just started using the setup again as the temps are dropping, very happy with it.