Amazon has officially signed up Sony BMG to offer DRM-free music on its MP3 store. The company now offers music from all four of the major record labels and can finally compete on the same level as Apple's iTunes service.

Sony BMG's library will be made available for as little as $0.89 (45 pence) per track. Sony's decision to make its library DRM-free on Amazon's service also allows users to copy the music an unlimited amount of times and add it to any player they deem fit.

Amazon with the advantage?

Perhaps most importantly, Sony BMG's addition to Amazon's MP3 store creates a significant difference between the industry leader - iTunes - and Amazon's own store. Namely, that Amazon is the only service to sell music from all four major record labels without copy protection.

Apple was the first to offer DRM-free music on iTunes through an agreement with EMI, but Amazon has quickly gained ground.