Wifi calling seems to work for me (Salt), the Wifi icon appears clearly in the status bar as well as during a call as an icon for calling and also during the call.
However, I have not yet been in a place where I would not have had a network (abroad, dead zone) and can therefore not say whether a normal call did not take place. But I don't think so, the voice quality sounds a bit different subjectively. If you have an idea how I could test this more precisely, I would be happy to try it out.
