The MIDI Manufacturers Association, also known as MMA is an organization where companies work together to create the standards that assure compatibility among MIDI products. Since 1985 the MMA has produced 11 new specifications and adopted 38 sets of enhancements to MIDI. Musical Instrument Digital Interface, or MIDI, is a system designed to transmit information between electronic musical instruments. ...
MIDI ring tones sound far better because they are polyphonic (play more than one note at one time) and because they use music synthesizers which produce a wider variety of sounds than possible before.
And since each instrument in a MIDI performance is separate from the rest, its easy to "solo" (listen to just one) individual instruments and study them for educational purposes, or to mute individual instruments in a song so that you can play that part yourself.
MIDI files are perfect for practicing with, as well as for performing when additional musicians are not available.