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division noticed some inordinately lengthy calls to an out-of-area directory information number. The calls were from a studio at Washington State College. When Bell’s engineers went to investigate they found what they described as ‘a strange-looking device on a blue metal chassis’ attached to the phone. They immediately nicknamed it a blue box.

The colour of the device was incidental, but the name stuck. The strange machine’s purpose was to enable users to make free long-distance calls. It was a huge advancement on simple loop-around-pairs: not only could the blue box set up calls to any number anywhere, it would also enable the user to roam through areas of the Bell system that were off-limits to ordinary subscribers.

The blue box was a direct result of Bell’s decision in the mid-1950s to build its new direct dial system around multi-frequency tones — musical notes generated by dialling that instruct the local exchange to route the call to a desired number. The tones weren’t the same as the notes heard when pressing the numbers on a push-button phone: they were based on twelve electronically generated combinations of six master tones. These tones controlled the whole system: hence they were secret.

Or almost. In 1954 the Bell System Technical System Journal had carried an article with the unpromising title ‘In-band Signal Frequency Signaling’ which described the electronic signals used for routing long-distance calls around the country, for ‘call completion’ (hanging up) and for charging. The phone company then let the rest of its secrets out when the November 1960 issue of the same journal described the frequencies of the tones used to dial the numbers.

The journal was intended only for Bell’s own technical staff, but the company had seemingly forgotten that most engineering colleges subscribed to it as well. Belatedly realizing the sensitivity of the information, Bell tried to recall the two issues. But they had already become collectors’ items, endlessly photocopied and passed around among engineering students all across the country.

Once Bell’s tone system was known it was relatively simple for engineering students to reproduce them, and then — by knowing the signalling methods — to employ those to get around the billing system. The early blue boxes used vacuum tubes (the forerunners of transis-

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