In a move that could serve as a death knell for DRM (digital rights management) as the defining feature of digital music's first decade, all four major labels have signed on to Amazon's MP3 download store.

Amazon MP3 beta.

Sony BMG Music Entertainment is finalizing plans to sell songs through Amazon without the copyright protection software that has long restricted the use of music downloaded from the Internet, BusinessWeek.com reported today. That news comes on the heels of Warner Music Group's decision late last month to join the Amazon store, a stark departure from the company's stated allegiance to using DRM to prevent piracy.

The other two major labels, Universal Music and EMI, signed on to Amazon's digital store when it launched its beta version in September 2007.

The use of DRM--designed to limit what a consumer can do with a legally purchased digital song in an effort to limit file sharing--became the defining issue in the music industry in 2007. Apple chief Steve Jobs' manifesto against the use of DRM in February 2007 and Amazon's launch of DRM-free store served as the two biggest blows to the use of DRM.

But labels have been slow to move away from DRM for fear that selling MP3s will increase file sharing and hurt sales. But with CD sales continuing to stagnate and with consumers flocking to music without restrictions, labels have been forced to reconsider.

Bronfman: A change of heart.

Details of Sony BMG's plans are expected to emerge in the coming weeks. Justin Timberlake, who is signed to the Sony-owned Jive label, is participating in a Super Bowl promotion with Pepsi that will kick off February 3 and offer free distribution of 1 billion songs from major labels, including Sony BMG, through Amazon's DRM-free download service, BusinessWeek.com reported.

Sony has been experimenting with DRM-free songs for about six months. The company began giving away DRM-free promotional downloads for recording artists who sell less than 100,000 units, and at least one artist gained mainstream exposure through the effort.

Warner's decision to join Amazon is noteworthy given CEO Edgar Bronfman Jr.'s vocal opposition to selling music without DRM. Sony BMG's move, meanwhile, is a major reversal for a company that drew heated criticism and fines in 2005 for its use of "rootkit" software on its CDs that acted like spyware when a CD was loaded onto a computer.