Apple watch
If I have my cellphone through one service will my watch that is through another service be compatible?
Question marked as
The watch shares the phone's SIM. It can't have service from a different carrier.
If you mean that you previously used the watch with a different carrier, that's a slightly more complicated question. I know Verizon used to have problems activating watches that had previously been active on another carrier. Contact your carrier and ask them.