A month after a study released by The NPD Group rated iTunes as the second biggest music retailer in the United States, Apple’s store has made it to the first spot.

The data released by The NPD Group are based on NPD’s Digital Music Study, which is s an annual survey of US consumer’s demand, and NPD MusicWatch, that racks past seven-day music purchase habits of the US population age 13 and older.

The iTunes Store became the largest music retailer in the US based on the amount of music sold during January and February 2008. Apple’s iTunes surpassed WalMart, which last month had the first place.

“We launched iTunes less than five years ago, and it has now become the number one music retailer in the world,” said Eddy Cue, Apple’s vice president of iTunes. “We are thrilled, and would like to thank all of our customers for helping us reach this incredible milestone.”

In late February, Apple announced it has reached the four billion sold songs milestone and it has 50 million customers worldwide. iTunes Music Store opened in April 2003 and the one-billionth song was purchased in February 2006.

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.

However, being rated as the biggest music store is indisputable a big achievement for Apple, but it remains how the competition will react to this news.

Today MySpace unveiled a new iTunes rival, MySpace Music, an online music portal/store which will not only sell digital music, but also concert tickets and merchandise. Still despite huge audience it remains to be seen if the new service will manage to surpass iTunes.