According to Lynn La at CNET: “AT&T has finally rolled out its native Wi-Fi calling feature on certain smartphones, after the Federal Communications Commission granted the wireless carrier’s waiver request for the feature. Starting Oct. 8, AT&T customers with the latest phones, the Apple iPhone 6S and 6S Plus, as well last year’s iPhone 6 and 6 Plus, can make and receive calls using a Wi-Fi network as long as the handsets are also running Apple’s latest mobile operating system, iOS 9.

Wi-Fi calling can be useful whenever users find themselves in an area with weak or no carrier coverage. By using a local Wi-Fi network, such as the one set up at your house or available in a public space like a cafe or library, you can still make calls without a cellular connection. And because the feature is baked into the devices themselves, you and the person you are calling won’t have to download a third-party app or service.

Out of the four major U.S. carriers, AT&T is now the third to roll out Wi-Fi calling, following T-Mobile and Sprint. AT&T hoped to launch the Wi-Fi calling feature last month when Apple first released iOS 9. Last week, the carrier accused the FCC of dragging its feet on approving the waiver it needed to offer the feature. The FCC, which denies the claim it was slow to OK the request, granted the waiver Tuesday.

In addition to T-Mobile, Sprint and AT&T, a number of Wi-Fi only carriers default to Wi-Fi first before connecting to a cellular network. These include Republic Wireless, Scratch Wireless and Google’s nascent Project Fi, which launched in April and is compatible with the Google Nexus 6P, 5X and 6.”

Here’s what you need to do to begin using AT&T Wi-Fi calling on iOS 9:

• Launch the settings app
• Scroll down and select Phone from the list of options. (You can also search the Settings app for Wi-Fi Calling if you so desire.)
• Select Wi-Fi calling from the top of the list.
• Slide the Wi-Fi calling switch to the On position.

Also from CNET: “The next few screens will require you to confirm you want to enable Wi-Fi calling, as well as opt-in to the service. The biggest warning is in regard to emergency services. You’ll also be asked to verify the address where you plan on primary using Wi-Fi calling, again, for emergency purposes. If the service isn’t available for your device yet, you’ll receive an error page explaining as much but not until you’re done with the setup process, which is odd.

After activating Wi-Fi calling on my iPhone this morning, it took about an hour for the “Wi-Fi” indicator to show up next to the carrier name atop my device.

As for placing or receiving a call over Wi-Fi, you don’t have to do anything different. Your iPhone will handle it for you; just pick up the phone and dial.”