Labeled a “public beta,” Amazon MP3’s inventory consists of nearly 2.3 million unprotected songs. The store boasts of having music from more than “180,000 artists and over 20,000 labels” with EMI Music and Universal Music Group providing major label tracks, and music from several indie labels, including Alligator, Sugar Hill, Rounder, Sanctuary and HighTone, make up the rest of Amazon’s catalog.

Because Amazon MP3’s inventory is not protected by any digital rights management technology, customers can play their purchases on any personal music player. That feature, combined with Amazon’s online marketing know-how and the company’s massive presence on the Internet may result in tougher, more vibrant competition for Apple and its iTunes Music Store.

“Amazon MP3 is an all-MP3, DRM-free catalog of à la carte music from major labels and independent labels, playable on any device, in high-quality audio, at low prices,” said Amazon VP for Digital Music Bill Carr. “This new digital music service has already been through an extensive private beta, and today we’re excited to offer it to our customers as a fully functional public beta. We look forward to receiving feedback from our customers and using their input to refine the service.”

Most songs available on Amazon MP3 are priced from 89 cents to 99 cents. The top 100 best-selling songs are priced at 89 cents, and most albums carry prices ranging from $5.99 to $9.99. The top 100 albums are priced at $8.99 or less.

For comparison, iTunes prices DRM-protected tracks at 99 cents, unprotected tracks at $1.29 and all albums, both protected and unprotected, at $9.99. So far, only one major label – EMI Music – has given iTunes the green light to sell DRM-free tracks.

Carr said some labels include a digital watermark with their MP3 tunes to track which company sold which song, and that Amazon does add its own name and the item number to a song to aid its customer service department. So, while the tracks are unprotected, it does appear that a pirated track could be tracked down to the point of purchase. Carr said it would be up to the customers to use the music legally.

No other store on the Net carries a brand name as recognizable as Amazon, and it’s easy to imagine customers picking up a few MP3s while they’re purchasing books, toys, or even physical CDs. What’s more, chances are anyone who has purchased anything online has probably already bought something from Amazon, meaning they are already registered with the company. For them it’s click, download, play. It’s that simple.

By selling unprotected MP3s, with many of the tracks marked below iTunes standard prices, Amazon MP3 may quickly succeed where others have failed. That is, giving Apple, iTunes and Steve Jobs a serious run for the money – at 89 cents per unprotected track.