asks: "While watching TV on my TiVo, I actually stopped to see an ad for a device called 'The TeleZapper', which claims to foil tele-marketers by convincing their auto-dialers that your number has been disconnected. The FAQ is light on technical details, only mentioning that the device 'emits [a] tone briefly when the line is answered'. I'm hoping Slashdotters with more telecommunications expertise can enlighten me as to: how/if this might work and whether or not it is something I could reproduce with a sound card, say for recording at the beginning of my voicemail message. Could it be as simple as playing back the three shrill tones I hear when I dial a wrong number?"
Ah, the telephone equivalent to SPAM
. Too bad phones don't have the equivalent of procmail filters.