I've been using the TiT app for a week now on my LG G3, at first I selected my home WiFi to use the app because I don't get a very good signal in my kitchen, but I don't like the way it handles calls, it starts in loudspeaker mode as others have said, and it often sounds distorted the same way you would expect if you were on 3g and didn't have much signal, my connection is strong with my router. I also had a problem when someone called me, as I was in the call, I could still hear the phone ringing.
The other problem is the permanent notification in the notification menu, even when I turn the notification icon off, the notification telling me "mobile calling ready" stays there taking up valuable space. If I block notifications from this app in android, will I still be able to use 4g calling?