I think I have just managed to find my answer. Will test it later today.
The phone must still be switched on and connected to either Wi-Fi or
Cellular Network and the watch apparently still works. If the phone is
out of battery, then it will not work...
Hey @Milkybar-12 did you get anywhere with this? I am having the
similar, if not the same, problem. I have a data plan for my S24 Ultra
mobile and another plan for my Watch Ultra. They were both purchased
from O2 and both show O2 network. I have foll...