Performing rights organization BMI has released data on US ringback tone services from 2008 along with projections for '09.

According to BMI, revenue from ringback tones, the music a caller hears while waiting for the call to be answered, totaled some $205 million last year, up from $140 million in 2007. The organization's forecast has sales topping $235 million in 2009, up 15% year-over-year.

There's still a whole lot of room for growth in this nascent market. BMI figures that some 10 million US consumers have signed up for a ringback service, which is only about 4% of mobile subscribers.