I agree it's "pointless" but in retrospection I've done a lot of pointless things with computers. This sounds like fun.
"AnonymousApril 23, 2009 at 9:43 PM
Clever... but were you aware that someone already did it and you might already have the drivers on the machines? Linux's AX.25 drivers include a soundblaster interface. AX.25 uses frequency-shift keying (two different tones for 1 and 0), and transmits around 1200bps.
It is intended to be connected to an amateur radio, but can be hooked up from line-in to line-out if you want."