Wi-Fi calling is a new feature of iOS 8 that's available initially to T-Mobile customers in the United States and EE customers in the U.K. What's more, it's coming to other carriers in the coming months. It lets your iPhone make and receive calls using Wi-Fi instead of depending on your carrier's cell tower coverage.
Here's how it works.
Wi-Fi calling depends on a technology alternately called Unlicensed Mobile Access (UMA) or Generic Access Network (GAN), depending on which technical paper you're reading. The technology enables your iPhone to make and receive phone calls using a regular Wi-Fi network.