The Xbox Music mobile is officially here, and it doesn't look half bad. Here's the Android version, which happens to be very similar to its counterpart on iOS.
Navigation on mobile devices
As far as interface goes, the iOS version is very similar to the Android version. One of the only differences is that the Android app lets you swipe between screens, while the iOS app (shown here) only gives you buttons to let you jump around.
With either a long-press or a tap on a menu button, you can add songs to playlists or collections. Unfortunately, doing so takes you to an Add screen, when a simple inline "+" button would probably work better.