Originally Posted by
rans6andrew
Could it be a service supplier issue?
Yes, it could.
I think you mean what’s generally called 'calling over WiFi'?
Although this is a form of 'Voice over IP', VOIP generally refers to voice calls using apps such as Skype or Whatsapp, or to the new 'fixed' handsets being handed out by BT as they decommission their analog network.
Ive been trying to enable Wi-fi calling on my phone for a couple of years. It works with every supplier's SIM I’ve tried except my own supplier's. I’m on a Family SIM plan and my daughter has a later model of the same phone as me. She was in the same situation as me until the manufacturer issued her phone with a software update from Android 10 to 11 at which point WiFi calling started to work for her. The same Android update was not issued to my phone.
So my conclusion is that phone hardware, phone software and service supplier are all involved, and it's impossible to find a definitive list of what combinations will work.
Good luck.