My last whinge on this topic.
In the Android world, you could improve security and effectively extend the life of the phone by installing a 3rd party ROM, eg LineageOS. Depending on the community and skills of interested developers, this could continue being updated and even included upgrades to new Android versions with new features for years after the manufacturer abandoned it.
But some phones have proprietary implementations for VoLTE and VoWiFi. Eg on my Samsung phone,.which will soon stop receiving Samsung updates, everything on any AOSP based ROM works except VoLTE and VoWiFi.
So, this effectively makes these 3rd party OS's useless. You won't be able to take or make calls.
I'm not happy about that, and make make sure my next phone purchase will have VoLTE etc available on AOSP