@dcmike
Well, sadly i don't know the direct link, but i bet you can get the info on the main telegram UT channel.
See here : https://forums.ubports.com/topic/7536/volte-voice-over-long-term-evolution/14?_=1679516132860
Edit : direct link is in the thread i gave you 😅
https://t.me/+Fvp5xF2fK-E2Yzcx
But read the thread still ^^