The great blue box phone frauds

The use of an electronic device called the blue box to exploit a loophole in the nation´s long-distance telephone network is recounted. To avoid long-distance charges, blue box users first dialed long-distance directory assistance, 800 numbers, or numbers that carried only a small toll charge. After the user dialed his number and was connected to a long-distance trunk, the blue box emitted a 2600 Hz tone, clearing the equipment at the tandem trunk´s receiving end and signaling the switching equipment that the call had been completed and the trunk was waiting for a new call. The local central office, however, had not received its call termination signal, so the local central office did not disconnect the caller from the long-distance network. The permanent solution to the blue box problem proved to be common channel interoffice signaling (CCIS), a method rejected in the 1950s as too costly and difficult to implement.<>