A blue box is an electronic device that replicates the tones that were used to switch long-distance telephone calls. They allowed you to route your own calls and bypass normal telephone switching and billing. Blue boxes no longer work in most countries, but they can still be used with Project MF!
Please see the Project MF Blue Box page for details on building your own blue box, especially if you received a blank PCB at The Last HOPE conference.
The completed blue box can be used to legally phreak calls on the projectmf server.
See www.projectmf.org for details.