PlayStation 4 Companion App Available
The app lets you use your phone/tablet as a second screen in conjunction with supported games, chat with PSN friends, use your phone/tablet as a keyboard for your PS4, receive game invites, purchase games for your PS4, and more.
The app is free.
It may sound weird, but I'm actually more excited for some of the remote functionality this app provides more than using my phone as a second screen in games. I know I'll use it a lot to buy games when I'm away from my system and as a keyboard when chatting, etc.