Nokia Music is not available in ALL countries. AFAIK for example, in North America, it's only launch in USA but not Canada.
So depending on where you live, it may not have been launched yet in your region.
I know it's widely available in Europe because Nokia is a Finnish company.
As an important side note, Nokia Music Rocks Big Time
I don't really listen to music alot but Nokia Music converted me totally.
I really enjoy my music now more than ever, thanks to Nokia Music.
I really hope the app is made available to you soonest. Cheers