Unlike real-music ringers, polyphonic ringtones only simulate music using a pre-defined set of tones and instrument sounds. They cannot reproduce vocals or exact music. See: Real-Music Ringers ...

Elberse, Anita, Jehoshua Eliashberg, and Julian Villanueva. "Polyphonic HMI: Mixing Music and Math." Harvard Business School Case 506-009, August 2005. (Revised September 2006.) (Spanish version also ...