Originally Posted by
Mac Guy I don't think the Watches are carrie specific. I didn't have to specify a carrier when ordering my S3C. The Watch has works with your phone so will be on the same carrier as your phone. You can't use it on a different carrier than your phone. You move your phone to a new carrier, the Watch will follow.
But the carrier you move to must also support the watch. So far, none of the MVNOs do, and there are some regular carriers (US Cellular) in the US that do not. And, as has also been reported, there are individual models for particular countries and/or regions - three models in particular. If you move from the US to Canada, your Apple Watch will still work on a Canadian carrier. If you move to the UK, though, you'll need to get a new watch.
See
https://www.apple.com/watch/cellular/#mn_p for details on countries and carrier by model.
On a tangent, you have to have a phone to use the the Watch's cellular functionality. Besides being needed for initial setup, it's assigned the same number as your phone.
Well, you need a phone to use a watch, period. Celluar or not cellular.