iMelody was developed by the irDa association (infrared communications) as a standard file format for melodies. It has also been adopted as the ringtone format by the 4 companies developing the Enhanced Message Service (EMS), a smart messaging standard.

iMelody is a feature-rich melody format, featuring volume modifiers which can be used to vary the actual volume throughout a melody, special codes to flash a phone's backlight, LED or make it vibrate and other advanced features.

iMelody is used in some recent phones by Ericsson, Alcatel, Motorola and Siemens. As of summer 2001, a growing number of phones from these companies are expected to be able to receive ringtones over the air through an EMS message in the iMelody format.

Source: www.about.com