gt72 - I am sure some of the 'moving phones' were trains or coaches or passengers but (1) this is the US - "nobody" uses mass transportation after 9pm! in fact when I have used public transport in the US it appeared much less likely that people used their phones than in the UK. (2) my experience in the US is "everyone" uses their phone whilst driving with none of the 'embarrassment' you might get here. I'm not sure but it may not be illegal in some/all states. (3) you would therefore assume that at least SOME of the moving phone calls would be drivers - and expect if the phone causes accidents that there would be some correlation.
It is surprising though that a period of increased phone use even amongst travellers doesn't result in increased accidents.
Of course there are fewer children, pedestrians and cyclists around after 9pm. The roads are quieter, and of course US 'highways' are big open and straight and the risk factor of using a phone there may not transfer to a twisty back street. My own opinion is that "short" calls are worse than long ones too: once a call has a rhythm and the recipient understands you are driving some of the distraction may be reduced. This may mean that the logic of waiting for the 'free' call period is wrong.
The anecdotal evidence above would suggest (perhaps logically) that texting / emailing / surfing is possibly even worse than talking on the phone.
Footflaps - it was calls only not data / text etc.