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!
The ProjectMF server can be accessed via the PSTN on 630-485-2995. The switch will play back recorded instructions when you dial in. You must have a blue box handy and understand how to use it to have any fun with this.
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.
More info at www.projectmf.org