Spotify has said it will phase out its invitation-only system in the US. Facebook’s f8 announcement today of the Open Graph will allow Spotify users to listen along to music with their friends as they learn about their actions in realtime. Users will still need to sign in using their Facebook credentials to get free access to the service. Facebook listening will still count against the 10-hour monthly listening cap and listens-per-track limits if the member reverts back to the free service rather than subscribing to one of their premium plans. Spotify has more than two million Premium subscribers worldwide.