Social network MySpace lobbed a shot across the bow of Apple iTunes last night with the launch of MySpace Music, a new site that offers free on-demand music streaming along with MP3 downloads for sale to US users.

The joint EMI Music, Sony BMG Music, Universal Music Group and Warner Music Group venture, which MySpace announced in April, builds on the social network's roots by including new user-to-user sharing tools and new ways for musicians to sell music and merchandise.

Many initial reviews lauded the MySpace Music user interface and its business model, which aims to generate revenue from advertising from large companies like McDonald's, State Farm and Toyota, and through sales of merchandise and concert tickets.

Users can stream songs for free or purchase music downloads from a catalog of five million artists through the site, which is powered by Amazon's MP3 downloading service.

The first phase of the site includes a new "MyMusic" tool set to help users download, stream, and personalize their music content and create public or private playlists. Users can stream music from a friend's playlist on-demand. Users can also purchase DRM-free MP3s of any of those songs, MySpace said. "Buy" buttons on the site will allow users to purchase MP3s that are playable on all digital music devices including iPods, MySpace said.

Michael Arrington, a blogger at TechCrunch, said that MySpace has done "something incredible" for the online music business.

"They've created both a compelling music experience for users as well as a realistic, long term business model for labels and artists in a world where recorded music moves towards free," he noted. "Today, the labels have all but given up on DRM (Digital Rights Management), and users can now play virtually any song ever recorded on demand for free. MySpace has created the first ecosystem that has a shot of producing sustainable revenue streams for artists based on advertising, merchandise and concert sales."

If it works, he went on to note, the next step in the evolution of online music will be the decline of fees for per-stream feeds and downloads.

"Instead, labels will see music consumption for what it really is - free marketing," he added. "Labels will compete to encourage song downloads and streams to move those songs up the charts, attracting premium advertisers, merchandise sales and sold out concerts.