AT&T customers who updated their iPhone to iOS 9.3 received an unexpected free text message. The carrier has made it possible for those iPhones to use Wi-Fi calling internationally, meaning that AT&T customers can now place calls to and from the US without being charged for airtime.
The text (seen above) shows that the latest carrier software update takes the Wi-Fi calling capability and extends it outside of American borders. This means if you're on a Wi-Fi network somewhere in the world and make a call back home, that call is being made over the Internet and not on an international carrier's network. The result? No ridiculous international roaming charges.
However, if you're in China, Cuba, India, Iran, Israel, North Korea, Pakistan, Saudi Arabia, Sudan, Syria, Turkey, the UAE or Vietnam, forget it. The feature is restricted in those countries for the time being.
Wi-Fi calling is a blessing for those who are in areas with bad cellular service; I live in an area surrounded by hills that has always had one or two bar service, and Wi-Fi calling has made it possible for me to make and receive calls that used to drop. It's easy to turn on the feature. Launch the Settings app, then tap Phone > Wi-Fi Calling, and tap the "Wi-Fi Calling on This iPhone" button to turn it to the on position. The service works on the iPhone 6 and 6 Plus and the iPhone 6s and 6s Plus.