Why can't I cue up several podcasts on soundcloud or a book on audible.com (while stationary) and then listen to them while I drive?
If I can legally interact with a dash mounted GPS (or in-car Nav system), why can't I run a Nav app on my phone and mount it to the dash?
What would be really smart is a way to map some generic steering wheel mounted buttons to controls in the phone's nav app. This could easily be achieved over bluetooth, the same way that handheld Powerpoint presentation devices emulate the PC keyboard and allow presenters to drive their slideshow from the remote.
Steering wheel buttons could get mapped to the Google Maps app for Zoom In, Zoom Out, Volume Up, Volume Down, Mute.