Simplify the following text for a Grade 9 native English-speaking person.
Original: As of 2006 , digital music sales are estimated to have reached a trade value of approximately US$ 2 billion , with tracks available through 500 online services located in 40 countries , representing around 10 percent of the total global music market .
Simplified: As of 2006 , digital music sales are estimated to have reached approximately US$ 2 billion .