In the early days of the phone system, you picked up a telephone and talked to an operator who put your call through. As more people got phone lines, the phone company began to replace its operators with special switching equipment. When you dialed a number, your telephone sent a signal to the switching equipment, which routed your call to its destination. Such switching systems could handle more calls more efficiently than human operators, but they also opened the door to phone phreaking. Trying to trick a human operator into letting you make a free phone call to Brazil was nearly impossible, but tricking a mindless machine into letting you make free phone calls only required sending signals identical to the phone company's. If you knew the right signals, the switching systems would blindly obey your orders.
Perhaps the most famous phone phreak was a man nicknamed Captain Crunch because of his accidental discovery of a unique use for a toy whistle found in a box of Cap'n Crunch cereal. He found that blowing this toy whistle into his phone's mouthpiece emitted a 2600 Hz tone, which was the exact frequency used to instruct the telephone company's switching systems.
Other people soon discovered this secret, and some even developed the ability to whistle a perfect 2600 Hz tone. For those unable to obtain the original Cap'n Crunch toy whistle, entrepreneurs started selling devices, known as blue boxes, that simply emitted the 2600 Hz tone. With the introduction of personal computers such as the Apple II, phone phreaks started writing computer programs that could emit the proper 2600 Hz tone from their computer's speaker.
Blue boxes worked as long as the telephone company relied on their old electromechanical switching systems. But eventually these were replaced with newer electronic switching systems (known as ESS), which rendered blue boxes (and the infamous 2600 Hz tone) useless for manipulating the telephone system (although blue boxes may still work on older phone systems outside the United States).
Of course, the introduction of ESS brought a whole new set of problems. With the older electromechanical switching systems, a technician had to physically manipulate switches and wires to modify the switching system. With ESS, technicians could alter the switching system remotely over the phone lines.
Naturally, if a technician could perform this feat of magic over the telephone, phone phreakers could do the same—if they only knew the proper codes and procedures to use. Obviously the telephone company wanted to keep this information secret, and the phone phreakers wanted to let everyone know how the telephone system works (which is partly what the ongoing struggle between the telephone company and phone phreakers is all about).
To learn more about phone phreaking, visit one of the following phone phreaking websites: Hack Canada (http://www.hackcanada.com), Phone Losers of America (http://www.phonelosers.org), Phone Rangers (http://www.phonerangers.org), or United Phone Losers (http://www.phonelosers.net). Or try the alt.phreaking and alt.2600.phreakz newsgroups for messages about phreaking.