Sounds exactly like an option Apple will build into a future iPhone. Reminiscent of the max volume control on iPods. Would be a great feature for SJ to tout on stage, something no other phone has "built in". Simple addition to the Settings panel, what is allowed/disallowed when traveling at driving speeds.
Nice idea izup, but I predict you'll be Soundjammed by!!
It would have to be locked by a passcode so some teen couldn't unlock the settings