WiFi calling is a feature that allows you to make voice calls via a Wi-Fi network instead of using your carrier's network connection. This feature is especially useful when you're in an area with weak carrier coverage, such as when you're traveling to the residential countryside or in a building with spotty reception. All four major US carriers (T-Mobile, Sprint, AT&T, and Verizon) provide built-in Wi-Fi calling, and Republic Wireless and Google Project Fi provide Wi-Fi calling on certain phones too. Making calls over Wi-Fi can come out of your regular minutes allowance depending on your carrier and your phone plan.

The WiFi Calling Setting app is designed to enable the "Wifi Calling" function on retail mobiles that have the feature but not any menu entry to enable it. The app can check the hidden function and enable it if it can be used. To use the app, start it and click "Wifi Calling Setting," then click "WLAN calling," "ENABLE" WLAN calling, and "WLAN preferred." The app welcomes users to report compatible and incompatible phone models and incompatible phenomena, and they will further improve the app.

A full list of carriers that have added support for Wi-Fi calling includes Canada's Bell, Telus, eastlink, Rogers, Fido, and Virgin Mobile; the United States' Alaska GCI, T-Mobile USA, Appalachian Wireless, Unlocking, AT&T, Metro PCS, Ting, C Spire, Simple Mobile, Verizon Wireless, and Sprint Wireless; Austria's A1; Belgium's Telenet; the Czech Republic's T-Mobile and Vodafone; Denmark's 3, TDC, and Telenor; France's Orange and Bouygues; Germany's O2, Telekom, and Vodafone; Greece's Cosmote; Ireland's Eir; Liechtenstein's Swisscom; the Netherlands' Vodafone; Norway's Telia and Telenor; Poland's Orange, Play, and T-Mobile; Romania's Orange; Spain's Orange; Sweden's 3; Switzerland's Salt, Swisscom, and Sunrise; Turkey's Turkcell and Vodafone; and the United Kingdom's 3, O2, Vodafone, and EE.