The second largest mobile operator in the US has announced that it is extending its WiFi Calling service which it introduced last October in its domestic market (US, Puerto Rico and the Virgin Islands) to global markets. In order to enjoy the service while traveling overseas, AT&T customers would need to own either iPhone 6s, iPhone 6s Plus, iPhone 6, or Phone 6 Plus, all running iOS 9.3.
“You can make calls to domestic numbers and receive calls with no additional charge and no impact on voice call airtime usage,” according to AT&T. “For international calls, the rates from your calling plan or international long distance package apply.” This means that calls made to international numbers via the service will still be billed according to customers' rate plan.