Gaeilgeoir bitracer Should be, take a look here under "Devices with eSim"; Setting up & using Multi Device | Swisscom take care about the requirements for VoLTE mentioned above VoLTE: 4G calling – Help | Swisscom | Swisscom
bitracer Thanks, I also found this: https://www.swisscom.ch/de/privatkunden/hilfe/mobile/multi-device.html#accordion-3f344c3dcf%5Bselected%5D=accordion-3f344c3dcf-item-84159d06f3 It appears that from watchOS 9.1 it will also be possible to make calls in roaming with the Apple Watch.
