Internet, Wi-Fi and phone
VoLTE
Abbreviation for Voice over LTE
In short and in plain language
VoLTE is a way to make calls over a newer phone network.
Old phones without it use old networks for calls.
When those networks shut down, calls with such phones may stop.
Definition
VoLTE is a technology that lets a phone make calls over the LTE network, the fourth generation of mobile networks. Older phones without VoLTE fall back on older networks for calls. Once those are switched off, calling with such devices may no longer work.