Spotify had a wp7 app, but is was rather buggy. It won't install on wp8 due to screen resolution (you can Bing search on the phone for Spotify and it comes up but won't install).
Spotify says they are working on a new, and hopefully better, version of the app for wp8 rather then fixing the older app for whatever reason. Its slates to release sometime in 2013 so it will be a while.
Xbox music pass could work if you are willing to commit only to Microsoft products, there is no way to use it on Mac, Android, IOS, or UNIX, whereas Spotify is platform agnostic.