With the impaired charge, having the keys in your possession gives you care and control. Because you are impaired your judgement on whether to use or not use the keys is suspect.Agreed... I would be weary of just pulling off to the side of the road to use my phone, etc..
I'm not sure where the lines of "driving" actually are.. or if that precedent has been set by a court yet.. similar to how you can be charged for impaired just for being in the car, not running, with the keys in your possession type of thing.
Park and text is weasel territory. How is parked with only your foot on the brake preventing motion different than stopped at a red light or stopped behind a traffic jam? If you put the car into park it indicates a deliberate action to stop driving. Turning the engine off is a bonus indicator. The parking spot should be legal, not the passing lane of the 401, in front of someone's driveway, posted no parking zone, fire hydrant etc.