Just wondering -- is there a way to play a song in iTunes from the terminal app?
Scratch the word iTunes, then yes. 
Honestly, just look at its itunes --help output.
But most likely itunes will not even when started from a tty, but will work flawlessly if called from a terminal window.
(the first is all console, the 2nd is still GUI)
No idea about Mac, but have a look at these, if available:
aplay
moc
ffmpeg
mplayer
mpd
And if the arguments are too heavy, you might want to try my Video Handler Script (VHS), requires ffmpeg, which lets you play music from the console, and alot more.
Hope this helps, or be more specific.