@oldbutndy VoWiFi is still being investigated.
You could put your P3a on Droidian or Mobian/PostmarketOS and use SIP. UT devs are working on SIP integration in the dialer. It partially works now, but still needs a lot of work to be functional. In the meantime, SIP support is functional on those other OSes and would be the equivalent of VoWiFi.