AT&T debuts Wi-Fi Calling for Android with the LG G4 first to receive the feature
AT&T selected one Android handset to be the first to receive the new feature. The nation's second largest carrier chose the LG G4. If you are an AT&T subscriber who uses this device, be on the lookout for the notification that will tell you that Wi-Fi Calling has arrived on the handset. Once the service rolls out to the LG G4, users will not only be able to make or take calls over Wi-Fi, but send and receive texts as well.
Once the system is activated on the LG G4, and the phone is connected to a Wi-Fi network, it can automatically detect when AT&T's cellular signal is too weak to handle calls or texts. At that point, you'll be glad that you have Wi-Fi Calling.
AT&T says that the new feature is available to postpaid subscribers only, and the carrier adds that it will soon roll out the feature to more Android phones.
source: AT&T via AndroidandMe