AT&T's iPhone customers gain International Wi-Fi calling feature with iOS 9.3 update
Another new feature that came with the iOS update enables AT&T subscribers sporting a compatible iPhone, to use International Wi-Fi calling. Customers using this feature will be charged the regular price for the call. Texts can also be sent through Wi-Fi calling and count the same as a regular text message. Those using the feature are usually in an area where cell reception is poor. Using Wi-Fi calling allows them to use the Wi-Fi hotspot in place of the cellular pipeline to make calls and send texts.
Wi-Fi calling is available for the Apple iPhone 6, Apple iPhone 6 Plus, Apple iPhone 6s and Apple iPhone 6s Plus, and can be turned on in the system settings. Last year, the feature became available for domestic calls and AT&T is now expanding it overseas.
source: AT&T via Phonescoop