Back in the day
2600 hertz was the
frequency that
AT&T put on all of their
long distance lines so that they could distinguish between a
free line and one that was
in use. If a line had a 2600
hertz tone on it, then that line was
available.
A man named
John Draper realized that a
toy whistle he got in a
Captain Crunch box was able to easily
generate a 2600 hertz tone. Draper
figured out that he could
dial a
number, blow his
whistle, and make a
free long distance phone call to anywhere in the
world. He shared his
knowledge with the
phreak community and has hence forth been referred to as
Captain Crunch.
Now days
long distance phone companies use
Signaling System 7, which is a little more difficult to
phreak than just blowing a
whistle.