Which Apple Watch
I'm thinking about getting an Apple Watch but I am not sure about which one to get. I'm not sure which one to get between gps and gps +cellular. Also, would it work on Sky mobile?
If you are always going to have your iPhone with you, then the Apple Watch can do everything the Cellular model can do via the iPhone radios.
If you must be able to leave your iPhone behind but still make phone calls, stream music, send Messages to others, such as when running, swimming, etc..., then the Cellular model will do that.
NOTE: If can use music files stored on the Apple Watch while on a run, and do not need to make phone calls or send text messages, then the GPS model without your iPhone nearby can still track your run.
https://support.apple.com/en-us/HT205547
