@atarilinux You don't need 5g yet, but eventually as they transition more and more bands to it, and the remaining 4g bands become too crowded. That is why I suggested the OP N10/N20/n200/N300 which are 5g capable.
As far as VoLTE, in the US, the device needs to be VoLTE capable, and if the device is not capable of reporting it's location directly to e911, then the user must register a service address with their carrier before VoLTE or VoWiFi will function. It will be quite a while before our e911 systems are upgraded across the board to make location tracking mandatory (because e911 was left to the counties to fund, and a good number of them do not have the resources to convert to an automated system).
You do need a phone that is carrier certified for Verizon or AT&T. T-Mobile just requires the device be capable. They do not keep white lists, only block lists.