There is a difference in what you are asking...

Polyphonic ringtones are much different from MP3s. This of polyphonic as that of an electronic piano, and the number of cords means the number of strings in the piano. The more cords, the more notes, thus more tones it can generate.

MP3s are just that of regular musical MP3s. A more realistic recording of whatever the file happens to be. This takes up a tad more memory space than that of polyphonic, but sounds more realistic than that of an electrical piano.

Hope that this clears things up and good luck an deciding on a phone.