The announcement follows after in May, iTunes was crowned as the biggest music retailer in the United States, based on the results from NPD’s Digital Music Study, which and NPD MusicWatch.

iTunes Music Store opened in April 2003 and the one-billionth song was purchased in February 2006.

However, the sales of iTunes have increased rapidly and the Apple’s music store has broken the 3 billion-song mark last July. That means that the company has sold almost two billion songs in less than a year.

According to NPD estimations, music spending declined 10 percent, from $44 to$40 per capita among Internet users, while the number of CD consumers dropped by one million in 2007 alone. At the same time, P2P music sharing continues to become more and more popular among teens.

As for Apple, it seems like the introduction of iPhone and new lineup of iPods, along with EMI’s catalog of DRM free tracks have boosted the music sales on iTunes.

In addition, in early 2007, Apple’s iTunes introduced a new feature called “Complete MyAlbum” thanks to which the music fans who purchased singles for $.99 a piece are able to get the full album they belong to at a discounted price.

What is also interesting to notice is that Apple said in its press release that the iTunes clients are toting up purchases and rentals of more than 50,000 movies per day. It’s the first time when Apple gives away apiece of information about its movies sales.