Sony BMG announced today that it will license its catalog to Amazon.com for the sale of unprotected MP3 downloads. This marks the fourth and final major music group to join Amazon.com's MP3 download store.

Earlier this week, Sony BMG unveiled its new artist-branded, MP3 gift cards that will be sold at entertainment retailers as well as grocery chains. Some of the criticism I read assumed the gift cards would be Sony BMG's only foray into MP3s. I never assumed that, and now we have the Amazon.com announcement to show that the gift cards are just one of many ways to purchase Sony BMG's MP3s.

There is no official word on when the catalog will be added. Amazon.com's main MP3 page is currently spotlighting a few new Warner Music Group titles; WMG announced it would drop DRM a couple of weeks ago.