A ring tone is the sound made by a telephone to indicate an incoming call. The term, however, is most often used to refer to the customisable sounds available on mobile phones. This facility was originally provided so that people would be able to determine when their phone was ringing when in the company of other mobile phone owners. Newer phones let the users associate a different ringtone for each phonebook entry. Newer phones can also use short pieces of music as ring tones, and the sale of these has become a major success of the mobile music industry.

Ring tone advertising campaigns have become hugely popular, though they have also attracted a great deal of criticism.

A phone only rings when a special "ringing signal" is sent to it. For regular telephones, the ringing signal is a 90-volt 20-hertz AC wave generated from the switch that the telephone is connected to. For mobile phones, the ringing signal is a specific radio-frequency signal.

An alternative to a ring tone for mobile phones is a vibrating alert. It may be useful:

in noisy environments
in places where ring tone noise would be disturbing
for the hearing impaired

Types of ring tone

Monophonic
Early phones had the ability to play only monophonic ring tones, short tunes played with simple tones. These early phones also had the ability to have ring tones programmed into them using an internal ring tone composer. Various formats were developed to enable ring tones to be sent via SMS text, for example RTTTL encoding.

Polyphonic
Polyphonic means that multiple notes can be played at the same time using instrument sounds such as guitar, drums, electronic piano, etc. Many phones are now able to play more complex polyphonic tones; up to 128 individual notes with different instruments are played simultaneously to give a more realistic musical sound.

Mobile phone handsets manufacturers have taken full advantage of new technologies to improve speakers in order to produce better sound quality.

Polyphonic ringtones are based upon midi or midi-like sequences so can pool in the 100+ different midi sounds, many polyphonic capable phones are able to play standard midi files, others play sp-midi which is scalable polyphony and depending on the number of channels the phone can play the handset will render that many notes. On an old polyphonic capable phone may play 4 notes at once with the flashier new handsets being able to render 128 notes at once. Many phones support SMAF (.mmf) files which is based upon a sound format devised by Yamaha.

Real sound ring tones
A new version of ring tones, often called either real sound ring tones, music ring tones, voice tones, mastertones, realtones, singtones or true tones, now use the Pulse-code modulation encoding of the real sound. The real sounds can be actual pieces of music, along with all lyrics and the entire song backing music, including backing singers. They are usually contained in compressed format such as AAC, MP3, WMA, WAV, QCP, or AMR that can be used as a ring tone on many Series 60, Symbian or smartphones. Many cell phone manufacturers are including voice ring tones on most of their newly released phones, including Motorola, Nokia and Sony Ericsson. The first real music ringtone was created by Richard Fortenberry and Brad Zutaut and was sent over the Sprint network. They were two of the founders of a company called Xingtone. It was from a song by the band Devo.

Popularity
Ring tones, along with operator logos, have proven a popular method of personalising phones ? a major industry has popped up to tailor to the desire of people to customize their phones, and newer phones include features to allow users to create their own tones. Many people enjoy their personalisation of the phones, but some find certain ring tones annoying in public.