There's a few things at play here: * https://support.apple.com/en-au/HT203032 https://support.apple.com/en-au/HT203032 WiFi Calling, which is (AFAIK) prioritis

There's a few things at play here: * https://support.apple.com/en-au/HT203032 https://support.apple.com/en-au/HT203032 WiFi Calling, which is (AFAIK) prioritised VoIP. Helps offload some calls from the provider's network which may help in congested areas * https://support.apple.com/en-au/HT203124 https://support.apple.com/en-au/HT203124 VoLTE. Voice over LTE, rather than GSM (?) channels. Highly prioritised VoIP over LTE data. Should improve call quality via better voice codecs. Seems to simplify tower equipment for the telcos - Telstra in Australia has some "4G Only" towers in a few places where "standard" voice calling is unavailable. VoLTE isn't particularly widely available here. Really happy to be corrected here - this is interesting stuff.