What's the threshold by which a phone isn't considered reliable enough to make emergency calls?

I've never personally had an emergency call fail on a Pixel device, and I don't know the broader statistics of how often they fail for other people compared to other phones. Do you?

For Australia, it needs to be on a whitelist.

https://isthisphoneblocked.net.au/

https://www.abc.net.au/news/2024-11-03/brand-new-phones-unab...