9600 Modem
From what I've read, there is a theoretical baud limit in every voice
telephone line of about 2400 baud, due to the fact that the typical voice
line has a useable bandwidth of 300HZ to 3.3KHZ (about 2400HZ).
Which, considering the quality of the average phone line between home
and the CO, it's amazing that any modulation can occur! And already
there's talk of dial-up 19.2K!