It is called critical mass.
When you have critical mass you can pull off just about anything.
How Twitter #Music works:
1. Users can listen to a few seconds of the (Popular, Emerging, Suggested, Now Playing, Me) music through iTunes Preview
2. To play full tracks users can select Spotify or Rdio and link it to their Twitter #Music account.
After allowing Twitter to access your information, you go through the dialogue to sign into your Spotify [Premium] or Rdio account.
I think Rdio is going to emerge the winner out of this collaboration because unlike Spotify, you don’t require a premium account with Rdio to run your Twitter #Music application.
How does Twitter make money in this? Twitter users like us will now stay longer #scratchhair
Where does this leave Pandora?
Enjoy the visuals!