Amazon.com has finally unveiled a beta version of its much-discussed digital music service, called Amazon MP3, offering more than 2 million DRM-free songs.

The service is almost entirely Web based, meaning no desktop application is needed to access the service. Customers have the option of downloading a small application that automatically saves purchased files in either iTunes or Windows Media Player.

Customers with existing Amazon accounts can simply pay for each track from their credit cards already stored with the system, and add digital tracks or albums to a cart that contains other products sold on Amazon.com as well.

As promised, there is variable pricing. Half of the 2 million tracks available cost 99 cents, while the other half are only 89 cents. More interesting is the variable pricing for albums, which range from $5 and under to $9. The service clearly advocates buying full albums over digital singles, and several artists that only will sell their work digitally as full albums -- such as Radiohead -- are present.

EMI Music and Universal Music Group remain the only two major labels participating, along with a number of independent labels, due to the lack of DRM.

All labels, of course, sell their physical CDs on Amazon.com as well.

Amazon shoppers looking for physical CDs will find links to the download service for those albums that are available digitally, an interesting cross-selling technique designed to promote the download service to those who may not even know it exists yet. In every case, the digital album costs less than the physical one.

Amazon did not give a timeline for how long the service will be in beta mode.