I live in an area with fair Verizon coverage, but in my neighborhood it's spotty. I'm a physician and I need to get calls from the hospital at night, but I can't get a signal sometimes in my bedroom. A few months ago, I solved the problem by using WiFi calling.
A few weeks ago, after upgrading to iOS 12, WiFi calling stopped working at my house. I've tried every trick I can find (airplane mode, turn WiFi back on, turn WiFi calling back on, etc..) and I spent a lot of time with VZW support who checked everything from their end and recommended resetting my network and then resetting everything (which was very annoying). Nothing has worked.
Strangely, I found that I could get WiFi calling to come on when I was at my hospital! So the function can work, just not in my house..? I've reset the modem and both of my routers with no luck.