When 2G and 3G are gone you will need VoLTE to make calls and a working IMS to send and receive messages. 4G is just for data. There is no native voice channel on 4G. VoLTE is a software layer a bit like having a VoIP app or WhatsApp running off you data for calls. It is obviously much more deeper integrated into your phone's firmware however.
In the video Michael demonstrates how the RTU5024 drops back to 3G when a call comes in. It immediately goes back to 4G after. This is because the modem cannot accept 4G voice (VoLTE) so the only option is for the network to use 3G or 2G.
This will be a massive problem for the industry once analogue phone exchanges (including 2G voice) are shutdown at the end of 2025.
All iot-portal and Priory Access products support VoLTE and IMS where appropriate.
Sorry for the poor video quality. It was quite unplanned and off the cuff!