IDC predicts the mobile market will hit $1 billion in the US by 2010 in "U.S. Wireless Music 2006-2010 Forecast and Analysis." I think they're far too optimistic and aren't considering innovations, such as WiFi phones, competition, and other options to download music to the phone. Phones will store thousands of songs. People will simply sync their phone to their PC, just like they do with iPods.

More from IDC:

"OTA mobile music storefronts are emerging as one of the most important new channels for fans to discover, purchase, and enjoy full-track music and related content. Despite the fact that barriers such as low consumer awareness, lack of widely available broadband wireless networks and devices, and business model uncertainties will constrain growth for some time, IDC's research suggests that the number of wireless full-track purchasers should eclipse the number of online music service users by year-end 2008. IDC also expects that OTA tracks at about $2.00 each will emerge as a sustainable price point as long as mobile storefronts are well-designed and offer a wide selection of music, and the music listening experience on the device is comparable to MP3 players."