Turn on Wi-Fi Calling to improve call quality and in areas with no cell coverage.
If you use AT&T, Verizon, T-Mobile, or Sprint in the United States with an iPhone 6 or newer model, you can turn on a feature starting in iOS 9 that enables your iPhone to send calls over a Wi-Fi network (and thus the Internet) rather than relying on spotty cellular coverage. It’s especially useful in thick-walled buildings that block cellular signals. To enable it, go to Settings > Phone > Wi-Fi Calling and run through a few screens that explain the service. You’ll be asked to provide an address, so your carrier can associate that address with your call if you make an emergency 911 call over Wi-Fi. (When you call 911 over a cellular connection, the 911 operator will automatically see your actual location; if you turn on Wi-Fi Calling and Wi-Fi is used for your emergency call because cellular won’t work, the operator will receive the address that you provided, regardless of your location.) Once you have Wi-Fi calling turned on in your iPhone, your devise will automatically switch between normal cell coverage and when you are located in a bad area for coverage, your iPhone will automatically switch to Wi-Fi Calling as long as you are connected to Wi-Fi.
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