Solved! Go to Solution.
I seem to have inadvertently fixed this issue on my Sony XZ1
Within the phone app, I went to 'Settings' | Calls | 'Accessibility'
I noticed TTY mode was set to 'off'. I set it to 'TTY full' and rebooted the phone.
Within the phone app, I can now see 'Wifi Calling' as an option within 'Settings' | Calls |
I'd be interested to know if this works for anyone else?