Table of Contents
Phone Phreaking Using In-band Tone Generators
| Field | Communications |
| Went Obsolete | 1980s to 1990s |
| Made Obsolete By | Out of band signaling for controlling phone switches |
| Knowledge Assumed | Being able to reliably produce the tones used to control phone switches |
| When useful | Before everyone had cell phones and the Internet was in wide popular use |
Early electronic switching and signaling systems in use on telephone networks starting in the 1950s and 1960s used specific tones to control various operations in a phone switch related to call setup and routing. One of the most well known tones was 2600 Hz.
People began building devices to reliably reproduce these tones into the mouthpiece of a telephone handset in the 1960s and 1970s. These were often referred to by colors, usually stemming from folklore surrounding the first device that performed a specific function.
These include (not an all-inclusive list):
- Red box - reproduces the tones generated by inserting coins into a pay phone to make free calls from that phone. Many pay phones either mute the mouthpiece until coins are inserted, or have a very narrow frequency filter that rejects those specific tones from the mouthpiece. Some payphones don't accept coins at all - calls must be placed using a credit card.
- Blue box - gave you the same level of control as an operator
- Black box - made free phone calls by seizing control of the trunk before a call is completed, and using it as a jump point for other calls. Telcos got wise to this by using exception flagging - a 2-hour call that never got completed to the intended party is not a normal occurrence.
Blue and Black boxing is pretty much extinct in areas with modern phone systems. Red boxes still work on some pay phones, but definitely on the decline.
