Verizon is turning on Wi-Fi calling for devices on its network next week, starting with the Samsung Galaxy S6 and S6 Edge. Additional devices — including iPhones — will be updated to support the service "early next year." Verizon is the last of the big four US carriers to flip the switch on Wi-Fi calling, perhaps in part because it waited until it could get an official waiver from the FCC to do it. AT&T also received a waiver (and also had some squabbles with T-Mobile over its lack of official approval).
Verizon is positioning Wi-Fi calling as part of its "Advanced Calling" feature, which is the branding the carrier is applying to both VoLTE HD Voice calls and its own video calling service. What's less clear is whether Verizon handsets will default to using Wi-Fi if it's available or if it will only resort to a Wi-Fi network "When a customer uses Advanced Calling on our 4G LTE network and travels outside of coverage," as Verizon's implies.
The Wi-Fi calling feature will require a software update for compatible phones — so if you have a Galaxy S6 or S6 Edge, keep an eye out for that next week (it's going to be rolled out "in phases," Verizon says).