http://www.theverge.com/2012/10/15/3504532/xbox-music-pricing-availability-microsoft-xbox-360-windows-phone-8-windows-8

Due with the new dashboard update tomorrow and installed by default on Windows 8 and Phone 8.

IMO The free ad-supported streaming could be the key to success - nice move!

Shame it isn't available for Phone 7 though.