If you want to compile it yourself (as I did), you'll have to find some patches that will let mpg123 know about OS X's sound system. I actually grabbed them from fink.sourceforge.net. I don't use fink, but they have a bunch of patches that they used to get stuff to compile. You'll have to dig around in the file list a bit before you find it. But it's there...somewhere...
Hmm...or I guess I could be nice and share mine with ya.
Just so the mods don't get fussy over that: it's a free CLI mp3 player.
Hey, if ya want the man file for it, let me know, and I'll put that on too.