I wonder why. I would think that it would be beneficial to offload voice traffic wherever VoWiFi is available for networks. Wonder why Vodacom does not do this and ask Samsung to implement VoWiFi as being always preferred if available. On my Vodacom Samsung even though the LTE signal was so bad I would have no bars, but would still cling to it and so Volte and phone would ring, but never would it just switch to VoWifi. Only if I put airplane mode on and then enable WiFi again would it then start using VoWiFi.
Strange.