We just updated our iPhones to IOS 9.3 and have turned on Verizon's Wi-Fi Calling service. We have good Wi-Fi in our house, in addition to access everywhere in our home to the cellular network using a network extender. I note that within our home the status bar on my iPhone sometimes says "Verizon" (indicating a cellular network connection) and sometimes it says "VZW Wi-Fi" (indicating Wi-Fi Calling connection). How is the choice between these two services made by the phone, or by by Verizon's CO? If it's a matter of signal level for the cellular network, what's the threshold for the cut-over to Wi-Fi Calling?