What is Dual-tone multi-frequency?
[[File:DTMF keypad layout.svg|thumb|Special DTMF keypad with extra keys]] [[File:DTMF dialing.ogg|thumb|DTMF dialing]] '''Dual-tone multi-frequency''' or '''DTMF''' is the group of special sounds a [[telephone]] makes when you push the buttons. Each number button makes a different sound. Telephone company equipment hears each sound and turns it back into a number. When all the numbers in a [[phone number]] are pushed the telephone company equipment will make the other person's telephone play a loud sound so they can answer their telephone and talk to you. Telephones also have a star (*) button and a pound (#) button. These buttons also make different DTMF sounds. These buttons can be used for other things like 'go' or 'do over'. But they are not part of the phone number. A few telephones have the letter buttons ''A'' ''B'' ''C'' and ''D''. They also make different DTMF sounds. Pushing the number buttons is called ''dialing'' the telephone. When a telephone makes a loud sound for you to answer, it is called ''ringing''. {{tech-stub}} [[Category:Telephone]]