While it’s still technically in beta, Google Music is an excellent service that’s completely free and now there is Windows Phone app to use it on the go. Using either a PC/Mac desktop app, you can upload up to 20,000 songs from your collection up to Google’s servers. Having done this, it can take a day or so to complete. Once installed, it will automatically upload tracks once you add them to your library. This provides you with access from any PC and now from your Windows Phone using Gooroovster.
Gooroovster is priced at $3.99 and it’s available now in the Marketplace. You can sign up for Google Music at http://music.google.com.