And despite the fact that my provider claims to support such a thing, and my phone supports it, I am unable to to use WiFi calling.
Your use case is not mine.
Don't pretend to have all the answers to a situation of which you are ignorant. It's unhelpful and unpleasant.
Edit: My comment was also unhelpful. I was going to delete it, but instead I'm going to leave it up and qualify my remarks by saying that your suggestion is a good one, and despite the fact that it's inappropriate to the circumstance, thank you.
Actually had to use WiFi calling yesterday and it just didn't work on my main #. Only my app based phone # (Google Voice) worked! That was a really unpleasant discovery since I had no cell service.
Definitely affirms what you are saying -- it doesn't always work! Yesterday was the first time I ever had a problem.
No errors or warnings, the calls just never go through.