‘Three’ (mobile phone company that is) says you can’t use their ‘Three in touch’ app for wifi calling on a dual sim phone (e.g. like FP2) with a ‘Three’ SIM. Three, of course, have never heard of Fairphone and offer no guidance, but it can be done with FP2. Vital if you live in a signal black spot. Here’s how it worked for me in the UK - I have no idea whether this app is available etc in other places, (discovered by trial and error so possibly some of these steps are not needed):
You should probably have the very latest software updates etc.
Remove the non 3 sim if you have one, switch off wifi, move into a ‘3’ 3G/4G signal area if you are not in one, switch phone off then on and you should be able to find, download and activate the ‘three in touch’ app from Google Play. You need to agree the various permissions. (I found the app would not even show up in Google Play without doing all this. Might also take a couple of tries to get the app to appear in google play.) Seems this is the only way to get the ‘Three in touch’ app onto an FP2 from Google Play.
Then move to your wifi zone and turn phone off and on and switch on the wifi function. You probably still can’t get the app to work as it should (it seems to revert to looking for a normal phone signal when you try to make a call) …but try opening the app, use the menu (three bars) at the bottom, choose ‘options’, scroll down and tick "keep wifi connection alive’ and bingo it worked…(goodness knows why!) It seems you can actually then replace the other sim card (if you have one) and activate it, ‘three in touch’ still seems to work ok.
The app then stays ‘alive’ in the top bar of the phone and is accessed by ‘swiping it down’ from the top of the phone. Seems to work pretty well - definitely better than O2’s now defunct ‘TuGo’ app. Let’s hope 3 keep this app alive, as others are making you buy one of their phones to get wifi calling to work.