Most mobile phones these days show on the status bar, and/or pull down menu and/or locked screen/screen saver when the Wifi calling has "kicked in" and therefore replacing cellular "calls" function. This only kicks in if the signal strength reaches a certain threshold (and that depends on the handset not the network).
So if you are just seeing "3" but not "3 Wifi callling" or similar means that your phone is still relying on the cellular coverage.
Sometimes to "force" wifi calling, I enable aeroplane mode and then activate only the wifi and 8 out 10 times works fine. The other 2 means Three is having problems 🙂 The annoying bit is that I need to remember to disable aeroplane mode when there is no wifi around/leaving home.
Although I've seen here and other forums lots of people struggling with their wifi router and handset wifi settings! More recently someone here was only able to get wifi calling to work after "forget the wifi network" and then add it again and then toggling wifi calling option from the settings. There's a lot to fiddle with, but as Paddiewack said, if you have a reliable broadband and Three is not having any problems, calls over wifi work as a charm.
