Originally Posted by
jonu
The problem I see (for iPhones, at least) is there is no way to turn off voice and SMS for one line only. Airplane mode accomplishes this, but then the local SIM would be off, too. Cellular data can be restricted to one SIM (or tuned off completely), but this doesn't restrict or turn off voice and SMS. You can turn one SIM entirely off, but then that number is not available for WiFi calling.
The dream would be to have the US (home) line fully off for connection to cellular radios (voice, data, SMS) but still "on" for WiFi calling (voice and SMS over data). Then use a local SIM, even a local data-only SIM, to fully access the US line as it uses the data of the local SIM. I don't think this is currently possible with the iPhone settings.
Yes, that's what you do. You just turn off data roaming and then force it onto a network that doesn't have a roaming agreement with the carrier. Then it will use the other SIM's data connection like wifi calling. The top of the phone will say "Verizon via Cellular Data" or whatever.