Yes @Anonymous it's correct that Vodafone have launched voLTE but it's only in a few key cities right now and on a Sony XZ on Nougat.
Cities are I believe > Glasgow, Edinburgh, Leeds and Inner London.
Samsung should push out an update to Vodafone purchased Samsung Galaxy S7 and S7 Edge devices, allowing 4G calling to be enabled.
A person will need:
WiFi and 4G Calling enabled on their account
A Samsung S7 or S7 Edge device with Android Nougat 7.1 software
The two models you mention should certainly be able to support voLTE but we're going to need to wait until these early stages have been completed to see if Vodafone expand the coverage and mobile phone models.
One place to watch is > Vodafone Blog.
Current Phone >
Samsung Galaxy s²³ Ultra 512gb Phantom Black.
