BMI estimates the U.S ringback tone market to be at $181 million for the year ended June 30, 2010. That represents a 7.2% decline from the $195 million (see graph) it calculated for a revised 2009 projection.

A ringback is a musical work that plays for a caller when they place a call to a participating mobile subscriber.

While sales have declined, BMI's data shows that the overall use of ringbacks has not diminished. "We believe that this is a result of the emerging trend of bundled services, where ringbacks are made available as part of a package," BMI senior VP of corporate strategy, communications and new media Richard Conlon said in a statement.

Also, BMI's analysis reveals that pre-pay services have held strong in the market, selling between 2.75 and 3.5 ringback units per subscriber in the first quarter of 2010, significantly outperforming traditional monthly billing-based services, which sold .25 to .5 ringback units per subscriber in the same period.

The ringback market shows there is an appetite for streaming-based mobile music services, which will move away from ringback and ringtones into a longer-form streaming mode, Conlon said.

"We are poised for another form factor and consumer behavior shift," he added. "This shift is driven by the increase in handheld data devices, enhanced content offerings and improved wireless infrastructure. The industry is coming into alignment to deliver new streaming-based services that we feel will equate to growth."

BMI's study, which is based on census data on the buying habits of 225 million U.S wireless subscribers, was announced Oct. 5 at the CTIA Enterprise and Applications Show in San Francisco.