I've been doing something else that works better for me.
I use the Pioneer Appradio2 headunit and just mirror evertything from my phone to the actual headunit screen.
It is a bit more expensive than the nexus 7, but in my opinion is a bit better, it also offers FM radio, and Ipod connectivity, Bluetooth and its a headunit so installations is easier.
as far as i now it only works with android phones. there might be something about iphones too...