I'm toying with doing this with my VXR8, the E1 (2007-2009 VXR8) has a pretty crappy proprietary head unit that has all the HVAC controls built in. I can't just remove it because it's all connected over CANBUS (a network between ECUs for cars typically built in the last 10 years), otherwise it immobilises the car. On top of that, there's no mounting kit for your typical single or double DIN head units. I'm gonna have to knock up a micro-controller circuit to "fake" the existing head units presence if I do this, not to mention work out how I'm gonna replace the HVAC controls. I'm thinking maybe write an app that runs on my ipad. But I digress.
Just a note on Internet streaming, it can be fairly stable if the following conditions are met;
a). You're not on O2, their network is poop
b). You've got a decent data package, you WILL chew through GBs of data, in the last 30 days I've used close to 3GB just listening to Spotify (with most of the files cached)
c). You're in a well populated area, such as a town / city centre, which normally has decent speeds for mobile broadband, the sticks tend to have crappy backbones, sometimes you might only get 2G or no signal at all
d). You're not doing more than 40-50 MPH (i.e. on a motorway), travelling at speed means constantly switching between cellular transceivers, which totally messes with streaming connections / downloads
So to summarise, if you're stuck in traffic in a town / city centre, it's perfect. Forget it for long distance trips