Making phone calls over a Wi-Fi network. Both the phones and carrier infrastructure must support Wi-Fi calling, prioritizing voice over data in the real-time environment of voice. With a single mode phone, users make calls only within a Wi-Fi hotspot. Dual-mode phones seamlessly switch between the cellular carrier and open or pre-qualified Wi-Fi hotspots.Wi-Fi calling was designed to eliminate dropped calls in areas where the cellular signal is weak. It also saves money for customers who have carrier plans with a fixed number of monthly minutes. Also called "voice over Wi-Fi," "Wi-Fi telephony," "wireless VoIP," and "voice over wireless LAN" (Vo-WLAN).Who's Doing It?By 2016 in the U.S., Verizon, AT&T, Sprint, T-Mobile and Project Fi (Google) supported Wi-Fi calling on selected smartphone models.Skype, FaceTime, Et Al.People are also able to make voice calls over Skype, FaceTime and various other apps, providing the recipients have the same program installed in their computers or mobile devices. See Wi-Fi, Wi-Fi Assist and Project Fi.