PlayStation Blog also mentions that folks will be able to sign up to the service using their PlayStation Network ID.
The Spotify service will be available in 41 markets. With that said, prior to the launch of Spotify, Sony's Music Unlimited service will close in all 19 countries on March 29, 2015. Sony mentions, "Nearly all of these countries will be among the 41 markets where PlayStation Music featuring Spotify will be available at launch, including the U.S., Canada, Mexico and Brazil."
Spotify is an ad-supported music service in its free version, with premium options beginning at $10 monthly. The company also recently added family plans for multiple users. This is a very cool addition to PlayStation for Spotify's 15 million paying subscribers and over 60 million active users.