AT&T has announced that it has enabled Wi-Fi calling for customers running iOS 9 on their iPhones. For those unfamiliar, Wi-Fi calling allows customers to place calls over Wi-Fi if they happen to be in an area where the standard cellular signal is patchy or unavailable. To enable the feature, you can navigate to the "Phone" section of your Settings app and flip the switch next to"Wi-Fi Calling." You'll then be taken through a series of setup screens where you can set your 911 emergency address and then activate the feature.
To recap, AT&T Wi-Fi calling was available for a short period in certain test locations when iOS 9 was in beta, but the feature didn't launch alongside iOS 9 because AT&T hadn't yet received a waiver to enable it from the FCC. Earlier this week, however, AT&T received the necessary waiver, and it now looks like everything is a go.
Keep in mind that you must have AT&T HD Voice features enabled to use Wi-Fi calling, and it can only be used in Puerto Rico, the U.S. Virgin Islands.