The fastest growing segment of the music business? Ring tones for phones. “Sales of mobile-phone ring tones, those tiny song recordings programmed into millions of cell phones around the world, jumped 40 percent in the past year to $3.5 billion, according to a study released Tuesday. The worldwide sale of ring tones, which started as a marketing gimmick for music labels and mobile phone companies, is roughly equivalent to 10 percent of the $32.2 billion global music market.”