We just switched from AT&T after 10+ years to Verizon because our Microcell and all 4 phones WiFi calling quit 2 weeks ago and nobody at AT&T could figure out why. Now I've got a similar problem with Verizon.
I ported my iPhone 8 to Verizon today and WiFi calling works if I'm in town using a separate T-Mobile WiFi hot spot and use Airplane Mode with WiFi on. I had enabled WiFi calling with a strong cellular signal and strong WiFi connection.
When I get home where there is no cell signal to speak of, the phone just sits there searching for a cell signal while it has a full strength WiFi signal good for 10Mbps download / 5Mbps upload.
I've reset network settings, rebooted our router, reactivated WiFi calling when I had a strong tower signal, and nothing has helped.
An iPhone SE 2020 ported from AT&T and a new Verizon-supplied iPhone SE 2020 also have similar behavior.
Does this sound like a network issue or an account setting problem?