Editing Blue box (section)

===Blue boxing===
The blue box consisted of several of [[audio oscillators]], a [[telephone keypad]], an [[audio amplifier]] and a [[Loudspeaker|speaker]]. To operate a blue box, the user placed a [[long-distance telephone call]], often to a number that was in the target area. Usually, this initial call would be to a [[toll-free telephone number|1-800 number]] or some other non-supervising telephone number such as [[directory assistance]].{{sfn|Rosenbaum|1971}} Using a toll-free number ensured that the phone being used for access would not be billed.

When the call began to ring, the caller would hold the blue box speaker over the microphone in the handset and use the box to send the 2600{{nbs}}Hz tone (or 2600+2400{{nbs}}Hz on many international trunks followed by a 2400{{nbs}}Hz tone). The called office interpreted this tone as the caller hanging up before the call completed, disconnected the call, and began playing 2600{{nbs}}Hz to mark the line free. However, this did not disconnect the call at the caller's end, but instead would leave the caller on a live line that was connected via a long-distance trunk line to a target exchange.{{sfn|Rosenbaum|1971}}

The caller would then stop playing the tone, which the exchange would interpret to mean the exchange's tandem was attempting to place another call. It responded by dropping its tone and then playing the flash to indicate it was ready to accept routing tones. Once the called end sent the supervision flash, the caller used the blue box to send a "Key Pulse" or "KP", the tone that starts a routing digit sequence, followed by either a telephone number or one of the numerous special codes that were used internally by the telephone company, then finished with a "Start" tone, "ST".{{sfn|Rosenbaum|1971}} At this point, the called end of the connection would route the call the way it was told, while the caller's local exchange would act as if the call was still ringing at the original number.