The most effective business card shared between today's innovative new online music services and the music industry seems to be a lawsuit.

The recently filed action against Project Playlist—by the RIAA representing nine major labels—is just the latest in a string of legal activity against online music services building their businesses outside of formal licensing relationships with record labels, dating all the way back to YouTube.

Project Playlist, as its name implies, allows users to build and share playlists of their favorite music. The service is fast, easy and very popular. It claims more than 24 million users, with around 600,000 unique visitors per day.

It does not host any of this music itself. Instead, Project Playlist links to music posted on thousands of third-party sites and allows users to stream from them all as a sort of aggregator. It only pays royalties to the performing rights organizations. As such, labels don't make a dime.

Other services playing a similar game of chicken include MP3Tunes, a digital locker service; and SeeqPod, a music search engine. Both are also being sued.

Whether Project Playlist, SeeqPod or MP3Tunes are breaking any laws has yet to be determined. To date, none of the music industry's lawsuits against enterprising digital services have reached a verdict, and as such there is no precedent. Instead, the industry and the service either reach a licensing agreement or the service goes out of business.

Labels involved in these lawsuits insist they have no desire to shut such services down. They only want to get paid for the activity. And the services, primarily startups, have no desire or ability to sustain a lengthy court battle.

Of the three currently being sued, only MP3Tunes—led by founder Michael Robertson, who has never shied away from a court battle—will likely proceed fully to trial and answer this question once and for all. Project Playlist at least seems open to dealing with labels. Sources say it is in early talks with Sony BMG—which is not a party to the lawsuit. Representatives from Sony BMG declined to comment.

Until then, there are a number of other music services growing in popularity while avoiding label licensing deals.

Click here to find out about three new music services ruffling the music industry's feathers.