I have successfully enabled wifi calling on my iPhone SE. It usually works fine, but on occassion, Verizon is unable to connect to the called number if I use wifi, but it can connect the called number via cellular. The error message I receive from Verizon is one of two (for the same called number, a toll-free number for home depot):
"Your call did not go through. Please try your call again. 159T"
"Welcome to Verizon Wireless - Your call cannot be completed as the called party is temporarily unavailable. Please try again later."
If I simply try the call using the cellular network, it goes through fine. However, the cellular network connection is pretty poor at my location, and sound quality suffers. So I prefer using the wifi network for calls.
It concerns us to hear you are unable to call certain numbers when using Wi-Fi Calling. It is important you are able to call without problems, and we will help. We have some questions to better assist. Does this occur when calling any toll-free number? Do you experience this issue when calling other numbers? DavidR_VZW