Dual-tone multi-frequency

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.

Category:Telephone