With the PlayStation App installed on your mobile device, you can:
· See what your friends are playing, compare trophies, and view your profile or recent activity.
· Chat with your friends; receive notifications, game alerts, and invitations, and then use your mobile device as an on-screen keyboard for your PS4™ system.
· Browse PlayStation Store, pick-up the latest hit games and add-ons, and then push them to your PS4 system so they are ready when you get home.
· Take advantage of the in-app second-screen features, when available, for greater challenges and control.
· Quickly access PlayStation system guides, manuals, and PlayStation.Blog.
A Sony Entertainment Network account and PS4 system are required to use all of this application's features.
I believe this is only available for North American gamers at present. That's what I'm hearing at least. I suppose it doesn't really matter since other parts of the world aren't getting the PS4 until later on anyway.