Shuhei Yoshida took the stage at the Sony TGS keynote to show it off on an Xperia Z1 phone. Hit "What's New" and you'll see updates from friends. Activities can be shown on the screen easily. He sent out a multiplayer invitation with a tap. Ustream and Niconico streams can be started from the device's app as well.
Under the Topics you can find official PlayStation information. Knack's page was shown off, complete with images and videos.
By connecting to the system the device can be used as a second controller or a second screen. Yoshida showed off an AR demo using the Xperia Z1 in addition to drawing software where he drew Knack. Flicking items from the screen threw them into the AR world -- very neat.
Finally, access to the PlayStation store is available via PlayStation APP. Multiplayer invites, Trophy info, verifying game purchases, and more are available.