I currently have two phones: My first (Ulefone Armor2) I had to ditch, because I could not get any Android upgrades beyond 7. The second I bought about a year ago (Umidigi Bison). We are with Vodafone and use their SureSignal technology to have cell coverage at home. Now Vodafone has decided to switch off the service asking their users to use WiFi calling instead. I would gladly do so, but somehow I can not activate the setting in either phone.
What I don't understand is:
Is WiFi calling a feature of Android, that can be included (or not) at the will of who ever makes the Android upgrade? If yes and say Umidigi does not do so, is there a way to use a third party Android to overcome this? What about "drivers" (for a better word - i come from a Linux world) to make the hardware of a specific phone work (camera, screen, fingerprint scanner etc)? Where to get a trusted Android version if the manufacturer is not forthcoming?

I have a gut feeling, that the carrier is also involved, as I see the same phone supported by 2D and not VF. The skeptic in me says yes, so they can sell their branded phones? OR does it take a new SIM card? I somewhere read, "just wait a little bit and the service became available?"

Anyone able to shed some light on this? I'd hate to spend $$ on yet another phone, while having two gathering dust, that are technically both working fine?!? Plus none of the ones on offer I have seen are 'rugged' phones...