I worked at T-Mobile and did some work on this very subject our studies showed that people are so addicted that unless there is a threat of jail time or drivers license suspension people will not put down their phones.
One is a few months of decreased mobility. The other is an entire life.
Consider that a plurality, if not a majority of the population is convinced that they're efficient at multi-tasking, and specifically that they can perform each task as well as in isolation. But we know that almost nobody multitasks well, period, and absolutely not with equivalent performance.
In addition, I believe the effective penalty for vehicular manslaughter is probably ten thousand times worse because of the psychological cost of being responsible for someone's death.
Make a phone-themed one!
</sarcasm>
Yeah, in practice it seems the only thing that will really work is license suspension.
That exact thing does happen to me. The drivers in my country are atrocious even if we do not consider the use of phones. Having to cross the street is quite stressful and do not dare to do so without running, even if I am in a another country with more sane drivers.