What is mobile ring tone?

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.
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 by the switch to which the telephone is connected. For mobile phones, the ringing signal is a specific radio-frequency signal.

Features
Whereas older telephones simply used a pair of bells for the ringer, modern ringtones have become extremely diverse, leading to phone personalization and customization.
Newer mobile phones allow the users to associate different ringtones for different phonebook entries. Many also allow users to create their own music tones, either with a "melody composer" or a sample/loop arranger (such as the MusicDJ in many Sony Ericsson phones). Often these are native formats only available to one particular phone model or brand. However, other formats, such as MIDI or MP3, are often suported; must be downloaded to the phone before they can be used as a normal ringtone. Commercial ringtones take advantage of this functionality, which has led to the success of the mobile music industry.

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

Criticism
Ring tone advertising campaigns have become hugely popular, though they have also attracted a great deal of criticism. For example, in May 2005 Jamster! bought 73,716 spots across all TV channels for the Crazy Frog advertisements, which were shown so often that many came to find Crazy Frog very irritating.