I know about that from https://support.apple.com/en-us/120000 but that has always only meant you can dial 911 through any cellular carrier even though yours is unavailable.

Is that what you mean? I suppose that helps if they then try 911.

This says satellite, but you’d have to know to do it: https://support.apple.com/guide/iphone/request-roadside-assistance-via-satellite-iph29bea54b5/ios

I always have cell service - can’t think of a way to test this?