Additional information : AppleWatch number is the same as the iPhone number. For this to work well, especially for alerts and notifications, the base number (iPhone and therefore also AppleWatch) must be reachable in roaming, especially in our neighbouring countries. Check with your operator (I had to modify my Swisscom contract!).

GPS and cellular yes. 4G I think yes as part of a Swisscom extension to my iPhone which is.

Oui, GPS, 4G, Wifi et Bluetooth.