The simplest method to access the telephone system anonymously is through a pay phone. One of the earliest ways phone phreaks learned to manipulate the telephone system was through telephone "color boxes." These boxes emit special tones or physically alter the wiring on the phone line, allowing anyone to make free phone calls, reroute phone lines, or otherwise raise havoc with the phone system.
Although the Internet abounds with different instructions and plans for building various telephone color boxes, just remember that many of them no longer work with today's phone system—although they might work in other countries or in rural areas. To satisfy your curiosity, though, here are some descriptions of various color boxes that others have made and used in the past. But first, a warning from a phone phreaker regarding the legality of building and using such boxes:
You have received this information courtesy of neXus. We do not claim to be hackers, phreaks, pirates, traitors, etc. We only believe that an alternative to making certain info/ideas illegal as a means to keep people from doing bad things - is make information free, and educate people how to handle free information responsibly. Please think and act responsibly. Don't get cockey, don't get pushy. There is always gonna be someone out there that can kick your ass. Remember that.
The surest way to catch a phone phreak is to trace his phone calls. One technique the FBI uses is called a Lock-in-Trace, which allows the FBI to tap into a phone line much like a three-way call connection. Because every phone connection is held open by electricity, the Lock-in-Trace device simply cuts into a phone line and generates the same voltage as when the phone line is being used. The moment you hang up, the Lock-in-Trace device maintains the voltage of the phone line as if the phone were still in use, thus allowing the FBI (or anyone else) to continue tracing the origin of a particular phone call.
The aqua box simply lowers the voltage level on a phone line, preventing the Lock-in-Trace device from maintaining the necessary voltage to keep the line open (and possibly even shorting out the Lock-in-Trace device itself). It should block any attempt by the FBI (or anyone else) to trace your phone call.
A beige box mimics a lineman's handset, which means that you can do anything a telephone company lineman can. Just open up any of the telephone company's protective metal boxes (usually found on a street corner), attach your beige box to an existing phone line (preferably not your own, which would defeat the whole purpose of the beige box), and you can make free long-distance calls at your neighbor's expense or eavesdrop on their calls.
Before you receive a phone call, the voltage in your phone line is zero. The moment someone calls you and the phone starts ringing, the voltage jumps to 48V. As soon as you pick up the phone, it drops to 10V, and the phone company starts billing the calling party.
A black box keeps the voltage on your phone line at a steady 36 volts so that it never drops low enough to signal the phone company to start billing—incoming callers never get billed for talking to you.
A cheese box tricks the phone company into thinking that your ordinary phone is actually a pay phone that can make outgoing calls but can't accept incoming calls. Cheese boxes were supposedly invented by bookies as a way of making calls to people while making it impossible for others (such as the police) to call them.
A crimson box is a device that lets you put someone on hold so that they can't hear you but you can still hear them. Great for listening to what telemarketers say to their co-workers when they think you're not listening.
The lunch box connects to an ordinary phone and turns that phone into a transmitter. That way you can use a receiver and eavesdrop on other people's phone calls while listening from a safe distance away.
Each time you drop a coin into a pay phone, the pay phone sends a tone over the line. When you toss in enough coins, the telephone company opens up the line so you can place a call. The red box simply generates the same tones that the pay phone generates when it receives a coin. By playing the tones from a red box into the mouthpiece of a pay phone, you can fool the phone company into thinking that you dropped coins into the pay phone, thus allowing you to make a free phone call.
Many of the above color boxes were developed to work with the older phone systems, which means they may not work with your phone systems. Of course, if you happen to live somewhere remote that hasn't updated its phone system, or if you're living in a country that still uses obsolete telephone equipment, you might experience better results. Since phone phreaking is about experimenting, you could try these telephone color boxes at your own risk and see what happens.