A dial tone is the signal that a person hears on a landline telephone before he dials a phone number. In most instances, the signal disappears once the first number is dialed. In most cases, cell phones do not have a dial tone.
This signal was widely established as telephone systems became automated, starting around 1947. Prior to that, a caller had to talk with a switchboard operator in order to connect with another party. When the operator was no longer necessary, many people assumed their phone wasn’t working because they heard no sound on the line. The tone was created so the caller knew that the phone was indeed connected and working before making the call.
At home or in an office, several phones can share the same telephone line. The use of the dial tone also eliminates confusion if one party picks up the phone and the line is being used elsewhere.
The early dial tone resembled a buzzing sound and was created by a motor driven machine. Today, the sound in North America is that of two interfering frequencies of 350 and 440 Hz (Hertz). These signals correspond to the concert pitches of “A” and “F” respectively. Most of Europe uses a single tone of 425 Hz.
The sound has also been adapted to let the telephone user know of voicemail or other calling features. This is done with a stuttered tone when the phone is picked up.
In general, cell phones do not use a dial tone. If the phone is off, then the user knows it is not in use since there is only one “line” per phone. The number can be dialed ahead of time, and the “send” button pressed. A recent incarnation of the cell phone, however, designed for older generations, uses this sound when the phone is opened.
Other common telephone tones include the disconnect tone that the telephone makes when the other party hangs up, the busy signal, and the loud tone that the phone makes when the receiver is off the hook. There are also several special information tones. These are the three-beep tones used by the phone company prior to the recorded messages that explain why the call did not go through.