Blue box : n. 1. obs. Once upon a time, before all-digital switches made it possible for the phone companies to move them out of the audible range, one could actually hear the switching tones used to   route long-distance calls. Early {phreaker}s built devices called `blue boxes' that could reproduce these tones, which could be used to commandeer portions of the phone network. (This was not as hard as it may sound; one early phreak acquired the sobriquet `Captain Crunch' after he proved that he could generate switching tones with a plastic whistle pulled out of a box of Captain Crunch cereal!) 2. n. An {IBM} machine, especially a large (non-PC) one.