After you start FRITZ!App Fon, it connects to the FRITZ!Box via Wi-Fi and remains active in the background from then on. Because the app runs in the background, you can make calls with your smartphone over the Wi-Fi network of the FRITZ!Box quickly and easily. In Android you can also close FRITZ!App Fon when you are not at home, for example. FRITZ!App Fon is always open in iOS.