Research group eMarketer predicts worldwide mobile music revenues will grow from $2.4 billion at the end of last year to $13 billion by 2012. Of this figure, $8 billion will come from ringtone and ringback tone sales, with $5 billion from full-track downloads. Additionally, it points to ad-supported programs as a likely growth market, from $42 million today to $1.5 billion by 2012.