According to market research firm NPD Group’s recent announcement, it seems that Apple’s iTunes became No. 2 music seller in the United States, just behind Wal-Mart Stores. The market research company based its recent report on measures of retailers’ volumes of sales.  

NPD Group said on Tuesday that Apple’s popular online music store reached the second place thanks to the large amount of music it sold in 2007. NPD Group started tracking music sold in the United States during the middle of 2006 and in the fourth quarter of that year it was Best Buy, not Apple’s iTunes, on the second place behind Wal-Mart Stores. iTunes was neither on the third place, which was taken by Target Corp. Apple’s online music service came only on the fourth place.

But in 2007, things changed and Best Buy took the third place and Target Corp. the fourth, while iTunes became No. 2

NPD Group’s analyst Russ Crupnick said this change was “fairly understandable given the pressure that’s been on CDs and the almost 50-percent growth in digital downloading in the past year.”

But the market research company’s recent report brought us also other interesting data to think about: the company showed, for example, that in 2007, almost 10 percent of music acquired in the United States was bought through legal downloads. During the same year, the number of consumers that bought digital music through legal pay-to-download web sites increased by 5 million to 29 million.

NPD Group also announced that the amount of music people bought in the United States rose 6 percent during last 2007.

In morning trading Apple’s shares fell $2.55 (2.1 percent), while Wal-Mart Stores’ shares rose to $51.14.