While hardware-wise absolutely capable of but still no smart phone has been able to provide a solution for a complete in-car companion device. You usually use your smart phone for 3 main purposes in your car:
1. Making/receiving calls
2. GPS Navigation
3. Playing music
You want your phone to provide these services at the same time and when they overlap it should take into account the priority. The priority of engaging the display and voice channel. For example you want the GPS navigator always have the priority of engaging the display but can be overridden by calls in terms of voice channel. Music has the lowest priority in both display and sound. When a new call comes in first of all I don't want it to take up the whole screen when GPS navigation is on and also it would be nice if I could take/reject it by voice. I want to have access to main music controls of the default player like next/prev/stop from GPS navigation screen and not to have to switch the app to do such things. Of course I can choose to have the GPS navigation working in silent mode when the music is playing.
Smart phones are getting armed with virtual assistants that could take voice commands but the problem is that you need to use your hands and run the app to make it ready to take your commands something that you don't want to do in you car, so my ideal smart phone will always be listening for a special voice command while working in "car mode" to get the virtual assistant activated just like normal assistants that wait for their name to be called to serve you! This feature is implemented in Vlingo for Android, you can say "Hey Vlingo" and then give your command but it doesn't work if another app like GPS navigation is running in the forground.
While GPS navigation is on most of the time while driving, I may decide to navigate to a different location, listen to a different play list or call someone which for all of them I have a shortcut in my 'Car Home' so another requirement would be smooth and quick switching between GSP navigation and Car Home.
If you have any idea/need from your experience of using your smart phone in your car put it in the comments.