Interesting... this made me go to the Apple site to see what TTY was all about. Apparently, to use a TTY machine, you need this adapter:
http://store.apple.com/1-800-MY-APPL...More=MA854LL/A
... for $19. Anyone wanna bet it does exactly what the $9.95 Belkin headphone adapter does? Or a $4 adapter off Ebay does? I could be wrong, but I'm guessing I'm not, and that's just wrong.