Well, I've got a basic command-line peal ringer working. It's stolen shamelessly from the Apple example code; I just pass a peal in from the command line and the code "rings" it via the built-in MIDI synth.
Minor nits: no ambience. A little reverb would be very classy. Possible to do, but I have to investigate the shipped-with-the-system AudioUnits a bit more to see if there's a really simple way to handle it.
A few more tweaks and I'll put it together as a