Popular social music network Last.fm said on Wednesday it is introducing a free service for fans to listen to their favorite songs on-demand. The new service is being launched in partnership with the four major music companies, as well as over 150,000 labels and artists.

When fans in the United States, Britain and Germany search for an artist on the Last.fm Web site, they can now stream the artist's song for nothing or pay to download an MP3 version of the song via Amazon.com

Terms of Last.fm's deals with the music companies were not disclosed.