What do you mean VoLTE is not supported on UltraHub / Wifi?
VoLTE is only on the Mobile Network -- = Voice over LTE (4G, Mobile Data, Mobile Network) only, not on WiFi / Fixed Broadband.
exactly - Volte is voice calling over 4g (usually voice on mobile phones goes over 3g)
The Ultra Hub is not a mobile device and doesn't run mobile voice calls. Its phone line uses SIP for voice.