I took this same app to other sounds (chainsaw, smoke detector) and it was all technically interesting. The modem tone was still the most interesting to me.
Take modem negotiation to a frequency display and zoom in, and you can actually see what the dual-tone in DTMF stands for. Heck, it looks like a piano roll if you want to take it in that direction for inspiration. Translate the row and column into a set of musical intervals and you'll be able to figure out how to play basic songs on your touch-tone phone.
Just tell me this isn't cool: http://imgur.com/sbtyY
I just found the first modem sound I could find off Google. By looking at the frequencies in the image, it is dialing 1-415-489-3565, which is still an active Earthlink dial-up number.
Small posts like this drag me in directions like this all the time. It leads me to questions I wouldn't have bothered with asking before today. This is absolutely within the guidelines and I thank the submitter for the enlightenment I received today.
So debate. I have used sounds and music while hacking. I know video game developers whose job title is "sound designer". This link, while not particularly advanced or profound, still inspired me to think about creating sounds in a way I hadn't before.
http://ycombinator.com/newsguidelines.html
Seems well within the guidelines to me.