2600 Hz

The tone that long-distance companies such as American Telephone and Telegraph used to indicate that the long-distance lines were open. This knowledge was used by early-day phreaker John Draper (a.k.a. Cap’n Crunch) and is the lead-in title for 2600: The Hacker Quarterly, a popular computer underground magazine.

See Also: Bernie S. (a.k.a. Edward Cummings); Draper, John; Goldstein, Emmanuel Hacker Icon (a.k.a. Eric Corley).