[toast0]

No wifi calling support? I had thought that was nearly universal?

Also, IIRC, LTE is mutually authenticated and your parents would not be able to attach to a private LTE network unless they have a SIM that's setup for it.

[ghilston]

Wifi calling unfortunately has its quirks even if it could be used

[azalemeth]

I've never got WiFi calling working despite my network nominally supporting it. I'd love a technical deep dive if you know anyone who has written it?