I also used to run a BBS. We had a small enough userbase (a couple hundred folks, with maybe 30-40 real diehards) and modem tones were unique enough above 14.4K that I could tell with reasonable certainty whom was calling in at any given time. I don't know if this would scale but it was pretty handy for freaking out anyone who happened to be hanging out in the computer room.

Also, at no point did I abuse my local console access powers to cause people to fly into heavily fortified sectors in Trade Wars. That would be mean.