The number of legal Napster-style music song-swapping services is set to rise as more websites sign important publishing deals.

Listen.com has inked a deal with the National Music Publishers' Association (NMPA) to pay advance royalties for music on its planned Rhapsody subscription download service.

The company is set to pay $500,000 to the NMPA's Harry Fox Agency licensing arm, which deals with 27,000 music publishers and more than 160,000 songwriters.

The Rhapsody music service is set to launch on 3 December combining on-demand playback and online radio.

Listen has yet to clinch a licensing deal with any major companies.

But Sean Ryan, its president and CEO, said: "This deal will allow us to launch Rhapsody in December with a large body of music from the independent label deals we have signed to date, and simplify the process for adding major label content to the service in the coming months."

Listen's arrangement comes hot on the heels of deals signed by other start-up music sites FullAudio and Echo Networks.

Echo Networks has signed up with AOL Time Warner while FullAudio has been given the license for Universal's music.

"Small companies have been looking into online services for a lot longer than majors, but without licences they haven't been able to do anything," said Ric Dube, of web analysts Webnoize.

"Now licensing deals are getting done. It certainly makes the labels look more friendly to outsiders."

There had been suggestions the big record companies were holding back from deals with smaller websites because they wanted to promote their own services, MusicNet and Pressplay.

MusicNet is the joint venture between BMG, EMI and Warner and Pressplay is backed by Sony and Universal. Both are set to launch by the end of the year.

The US Justice Department is investigating complaints from companies such as Listen.