Thanks for that GitHub link, menace690. It actually popped up in my Twitter feed just before you posted. Unfortunately, it necessitates a hardware mod, which I really can't be bothered to do for just one feature...
...but that's not the end of the story. Just days after assuming that this feature would pass me by, Messages asked if I wanted to receive text messages when my phone was on my network. A little after confirming this, my Mac started ringing. I'm still not sure if I was just mistaken about my hardware or what, but it certainly seems to invalidate this chart:
