According to BusinessWeek, Sony BMG is set to become the last of the four major record labels to, at least in part, ditch DRM. Motivated by the emergence of a genuine competitor to Apple’s iTunes – the Amazon MP3 store – Sony BMG will join rivals EMI, UMG and Warner to offer tracks unencumbered by copy-protection software.

Citing unnamed sources, BusinessWeek says that Sony BMG has joined Pepsi’s Super Bowl promotion in which one billion songs will be given away for free through Amazon. Justin Timberlake, signed to the Sony-subsidary Jive, is one high profile artist who will be featured.

While Sony BMG’s partial abandonment of DRM, along with the other three majors, is good news for consumers, it potentially provides a mixed bag for Apple. iTunes has so far been excluded from UMG and Warner’s DRM-free plans, with both companies’ favoring Amazon, in part because the e-retail giant is offering more flexibility in terms of variable pricing. If the BusinessWeek report is correct, Sony BMG looks like it will do the same. On the other hand, although a DRM-free world breaks the iTunes/iPod hegemony – since tracks bought from competing stores will playback on the iPod – it’s the hardware where Apple makes most of its money anyway. A more competitive and open digital music market will make Apple’s portable music player more compelling not less.

Also see: Digital music: 2007 year in review