Placing calls over longer distances required either operator assistance or provision of special subscriber trunk dialing equipment.
As the signals are audible tones in the voice frequency range, they can be transmitted through electrical repeaters and amplifiers, and over radio and microwave links, thus eliminating the need for intermediate operators on long-distance circuits.
AT&T described the product as "a method for pushbutton signaling from customer stations using the voice transmission path".
Other vendors of compatible telephone equipment called the Touch-Tone feature tone dialing or DTMF.
As a method of in-band signaling, DTMF signals were also used by cable television broadcasters as cue tones to indicate the start and stop times of local commercial insertion points during station breaks for the benefit of cable companies.
[6] Until out-of-band signaling equipment was developed in the 1990s, fast, unacknowledged DTMF tone sequences could be heard during the commercial breaks of cable channels in the United States and elsewhere.
[citation needed] Previously, terrestrial television stations used DTMF tones to control remote transmitters.
Initial pushbutton designs employed levers, enabling each button to activate one row and one column contact.
Public payphones that accept credit cards use these additional codes to send the information from the magnetic strip.
[citation needed] The signals *, #, A, B, C and D are still widely used worldwide by amateur radio operators and commercial two-way radio systems for equipment control, repeater control, remote-base operations and some telephone communications systems.
[citation needed] DTMF signaling tones may also be heard at the start and/or end of some prerecorded VHS videocassettes.
The encoded tones provide information to automatic duplication machines, such as format, duration and volume levels in order to replicate the original video as closely as possible.