Sony (NYSE: SNE) BMG will join EMI, Vivendi’s (EPA: VIV) Universal Music Group and Warner Music Group (NYSE: WMG) in selling music through Amazon’s (NSDQ: AMZN) MP3 store, making it the last of the major’s to start retailing DRM-free music, BusinessWeek suggests. The Sony/Bertelsmann JV had already been expected this quarter to start selling iTunes Store-like gift cards in stores, granting access to $12.99, MP3-format albums from a forthcoming website. BW’s unnamed source says Sony BMG will, around the same time, join the other labels giving away DRM-less tunes for free via Amazon in a SuperBowl-related promotion starting February 3. It’s not clear how much of the label’s catalog will be involved.

SEE ALSO: Warner Signs On With Amazon’s DRM-Free MP3 Download Store

Though none of the labels have abandoned DRM entirely (each has begun selling unlocked tracks in different ways, though all are now on board to support Amazon’s challenge of iTunes), this from Sony BMG would be indicative of the way the wind is blowing. Just two years ago, the label’s attempts to use rootkit software to control how consumers could play their CDs was lamented as spyware and a security risk. An unnamed Sony BMG exec said the label had experimented with selling DRM-free tracks for less well-known artists for six months: “A lot of these tests have led people to believe that maybe this works.”

Of the major four, EMI became first to try unlocked music in April, when it began offering a repertoire of DRM-free, higher-quality downloads through iTunes and, later, others. Universal followed suit in August, offering unlocked tracks to multiple distributors - but not iTunes - in a trial due to end this month. Warner announced it was joining the Amazon store over Christmas - the first of many such DRM-free distribution deals it is set to unveil. With all four majors on board, Amazon will now have a significantly greater shot at knocking off Apple’s (NSDQ: AAPL) crown. It’s worth noting the legions of smaller indie labels still command a large portion of global music sales, but Amazon claims the support of some 12,000 of them.