A blue box is an unauthorized electronic device that generates the same tones employed by a telephone operator's dialing console to switch long-distance calls. A blue box is a tool that emerged in the 1960s and 70s; it allowed users to route their own calls by emulating the in-band signaling mechanism that then controlled switching in long distance dialing systems. The most typical use of a blue box was to place free telephone calls. A related device, the black box enabled one to receive calls which were free to the caller. The blue box no longer works in most Western nations, as modern switching systems are now digital and do not use in-band signaling. Instead, signaling occurs on an out-of-band channel which cannot be accessed from the line the caller is using, a system called Common Channel Interoffice Signaling or CCIS.
Read more about Blue Box: History, Operation, Frequencies and Timings, Special Codes, Blue Boxes in Other Countries
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