Apple
iTunes Radio initially launched as a feature within the Music application on iOS devices. Being buried in the app has probably limited its success since it's easy to miss.
The interface, as well as the functionality for the standalone app will be basically the same as the one found inside of the Music application.
If iTunes Radio does get its own app, it would likely be better able to compete for advertisers.
As of October, iTunes Radio had 20 million unique listeners and 1 billion songs played. Meanwhile, Pandora had over 75 million active listeners in February, and continues to dominate 31% of the music streaming market.
The streaming music space is heating up as of late, with contenders like Pandora, Spotify, Beats Music, iHeartRadio and as of last week, Samsung's Milk.