In addition to the EAP-AKA' authentication, the strange and highly opaque ways through which VoWiFi support is signalled and enabled might be an issue here too.
I've seen brand new Pixel devices (which fully support VoWifi) act like they have never heard of the feature, until a special cell broadcast SMS is received from the carrier, to turn the feature on.
It would be interesting to see if you could manually tick all the boxes and open up a tunnel to the ePDG etc without that happening, but given the number of moving parts, and the differences between each network's implementation, I'd be sceptical it would work reliably.
(I'm pretty sure I had a situation where individual batches of IMEIs were being whitelisted for WiFi calling on another network, where the switch appeared, but VoWiFi didn't work... Yet on the Nexus device in question, one bought from the carrier directly did work. Even when you manually flashed both devices with identical firmwares from Google directly, this remained the case - must have been an IMEI whitelist or similar).
I've seen brand new Pixel devices (which fully support VoWifi) act like they have never heard of the feature, until a special cell broadcast SMS is received from the carrier, to turn the feature on.
It would be interesting to see if you could manually tick all the boxes and open up a tunnel to the ePDG etc without that happening, but given the number of moving parts, and the differences between each network's implementation, I'd be sceptical it would work reliably.
(I'm pretty sure I had a situation where individual batches of IMEIs were being whitelisted for WiFi calling on another network, where the switch appeared, but VoWiFi didn't work... Yet on the Nexus device in question, one bought from the carrier directly did work. Even when you manually flashed both devices with identical firmwares from Google directly, this remained the case - must have been an IMEI whitelist or similar).