The development means that consumers will be able to freely transfer music purchased through the site and play it on devices other than iPods and iPhones.
By the end of the quarter, Apple says that it will have 10 million tracks available without DRM.
Music that consumers have already purchased from iTunes can be upgraded to iTunes Plus, but there is an upgrade cost.
So far Apple has only released US pricing for these upgrades of 30 cents per track, 60 cents for a music video or 30 per cent of the total price for an album.
At the same time, Apple is introducing variable pricing to its digital download service. Currently tracks on iTunes in the UK cost 79p, but it will also introduce 59p and 99p price points.