The feature enables iPhone users to make and receive Wi-Fi calls on other iCloud-connected devices, including the iPad, iPod touch, Apple Watch, and most 2012 or later Macs, even if the iPhone is turned off or not on the same Wi-Fi network. The devices must be signed into the same Apple ID used on the iPhone.
AT&T, Sprint, and T-Mobile already support Wi-Fi calling on supported iCloud-connected devices, so Verizon was the last holdout among the four major carriers in the United States. The feature is also supported by smaller U.S. carriers MetroPCS and Simple Mobile and by a few other carriers internationally.
Wi-Fi calling on other devices may not be live yet for all Verizon customers on iOS 10.3 beta, but it should be ready in time for the final version.