Napster’s January announcement became a reality as of today: the online music service announced the availability of MP3 files, which are compatible with almost any portable device, including the iPod and the iPhone, and don’t submit to copyright restrictions and limitations. However, the conversion will not include its subscription music service, which will continue to have copyright restrictions.

Songs used to be submitted to DRM (digital rights management) in order to prevent illegal copy or distribution of songs, but the consumers completely disagreed with the music companies, and the system became highly unpopular.

As of Tuesday, Napster offers over 6 million tracks in MP3 format, the largest library of its kind, and comes as a response to Apple’s clear dominance on the market with its iTunes Online Store. The difference between the two is that Napster offers no limitations, while the iTunes tracks come with a Fairplay DRM which prevents them from being played on other devices than the iPod.

Challenging Apple’s iTunes Store is probably one of the hardest things to do at this moment, especially considering that it recently became the number one music retailer in the U.S. However, Napster’s escape “from under the DRM cloud,” how Chris Goroc, Napster chief executive, told Reuters, will give consumers the freedom to listen to the music they’ve purchased on virtually any device.

The DRM-free tracks will cost $0.99 each, and $9.95 an album, similar to the prices on iTunes. The decision to convert single tracks, as well as albums, into MP3 format, follows the steps of three of the world’s largest recording companies, Universal Music Group, Warner Music Group Corp. and EMI Group PLC, who submitted to the highly popular MP3 demand for music tracks.

Goroc said in a statement earlier this year that they expected a broader adoption of digital music, as the music industry began to support the format. Napster joins Amazon.com in offering MP3 downloads, although tracks in its subscription service will continue to be submitted to DRM.