I have WiFi calling enabled on my Samsung Galaxy Note 5. However, there are times that I cannot make or receive phone calls even though I'm connected to WiFi. If I turn on Airplane Mode then turn WiFi back on, I can then successfully make phone calls. Apparently, there was enough cell signal to prevent WiFi calling from engaging, but not enough cell signal to actually make a phone call.
This seems broken.
I'd think that if WiFi calling is enabled and I'm connect to WiFi, then:
All calls and texts use WiFi.
The phone stops the high-powered attempts to reach a cell tower that quickly drain my battery.