[Maursault]

Fundamentally, a blue box is, along with the essential 2600Hz tone, simply a DTMF dialer, like what is built into touch tone telephones, only it used operator dual tone frequencies, not the same dual tone frequencies used by touch tone telephones. You can't do much at all with a blue box unless you understand how the switching equipment that detected those frequencies worked, and that was only documented in unpublished Bell Telephone Company and then AT&T manuals, then subsequently by phone phreaks who either learned by trial and error or somehow came across one of those manuals. Blue boxes stopped working due to the change to digital switching equipment.

A red box, which emulates the tone that tells a pay telephone or a long distance operator that a quarter has been inserted, should still function, if you can find a pay telephone that still accepts quarters.