In 1957 a blind seven-year-old with perfect pitch named Joe Engressia found that whistling a certain note into a telephone made the line behave strangely. He had stumbled on the 2600 hertz tone the Bell network used to signal that a long distance trunk was idle. Because control signals traveled on the same channel as voices, anyone who could produce that tone could seize an unbilled line. John Draper later found the tone in a toy whistle from Cap’n Crunch cereal.

This episode traces phreaking from rotary pulse tricks to the birth of hacker culture. A 1954 Bell System Technical Journal article published the multi-frequency routing tones, and students used it to build blue boxes that turned a home phone into an operator’s console. A 1971 Esquire article spread the secret to Steve Wozniak and Steve Jobs. By the 1980s, modems, bulletin boards, and calling card codes had turned curious exploration into toll fraud.

• Before tones, teenagers beat padlocked rotary dials by tapping the switch hook in rhythm, since the exchange only counted interruptions in the current.
• Wozniak engineered a digital blue box and Jobs sold them door to door in Berkeley dorms for $150 each. Jobs later said there would have been no Apple without them.
• Abbie Hoffman helped launch a newsletter, the Youth International Party Line, that taught readers to dodge phone billing as political protest. It later became TAP.
• After the 1984 AT&T breakup, hackers ran overnight scripts that had modems guess calling card codes for new long distance carriers, and groups like the Legion of Doom and Masters of Deception traded finds on bulletin boards.
• The fix was SS7, which moved control signals to a separate channel. The last switch that could still be phreaked in the contiguous United States was decommissioned on June 15, 2006, in Minnesota.