Using a smartphone to accomplish stuff while a passenger in a car, bus, or train is often one of the better uses of time.  

And even as a driver, use of the phone for GPS navigation has become a major (valid) purpose for it.  Most cab drivers and tour guides use them for that purpose now, as well as millions of citizens. 

Ironically, I often use GPS navigation on my phone instead of the nav system built into my SUV because it's restricted with the similar "safety" mechanism you describe... it won't let anyone (including the passenger) type in an address while the vehicle is moving.  I get frustrated with it, so I just use my damn phone instead. Google Maps is better anyway.