The phone isn't a way to tell. Any carrier/service provider can carry a phone. They just need versions that work on their network. It will depend on what network the phone is running on now. CDMA phones will only run on other CDMA networks and GSM phones will only work on other GSM networks. And of course the phone must be unlocked to switch to another network. However, those two, CDMA and GSM, are not swapable. The phone will run on one or the other. Like AT&T is GSM where as Sprint is CDMA.
These links list the carriers/service providers that run on each network. Compare the one the phone is on now to the one you want and see if they run on the same network. If they do, I would still check with the carrier/service provider you want to change to and confirm the phone will work on it.