How hackers tricked the US phone system using simple musical tones

While a 2600Hz tone could get you free calls, MF-ing an exchange could get you a whole lot more. For example, you could set up and run a conference facility on an exchange that enabled other phreakers from across America – and even from around the world – to secretly swap the secrets that they had learned.

The devices they built to generate these tones were called 'blue boxes'. With a battery-powered blue box, a phreaker could surf the US telephone network from a roadside payphone. Fraser Lucey was one such phreaker.