The mobile music market is expected to reach $676 million in 2014, up from $143 million this year, according to a report from researcher eMarketer.
With the number of mobile music listeners expected to grow from 21.7 million this year to 52 million in 2014, eMarketer estimates paid revenues from subscription streaming services and full-song downloads to increase 55 percent from 2009 to 2014 reaching $501 million that year.
Ad-driven revenues, which help support the popular free version of Pandora, for example, will bring in $44 million this year, about 31 percent of total mobile music revenues, the firm reports.
"The mobile music market is in the midst of a major transition," said Noah Elkin, senior analyst at eMarketer. "As the traditional revenue staples -- ringtones and ringback tones -- cede in relevance, streaming services have moved to take their place."
See also: "Mobile Video Ads Set to Soar"