I'll note that most of the calls that I get are
not from people in prison, nor are they life-or-death situations. They are not emergencies, and they are not once-in-a-lifetime opportunities. They are just ordinary phone calls. In fact, I'd wager the same is true for the majority of calls received by the majority of people.
U.S. DoJ figures give a prison population on the order of 2.3 million, while the
U.S. Census Bureau gives a total population of over 300 million. Thus, if an inmate only has one call per day, the "call from an inmate" scenario applies to less than 1% of the U.S. population. Those to whom it does apply, and who cannot bear to miss even one day, must surely engage in more, and more serious, lifestyle alterations to deal with that, so a change of driving habits would be a relatively small thing in comparison with the rest of the lifestyle alterations required to completely drop everything for 20 minutes on 20 seconds notice.
Given the small population to which your scenario applies, and the low probability of a randomly-timed call coinciding with a time when one is likely to be driving, I submit that it does not outweigh the greater benefit of a ban on cell phone use in the car.
The simple fact is that most of us do not need the kind of immediate, on-demand accessibility that is expected of us. If I miss an exit, I take the next one. If somebody calls me about dinner plans, a broken computer, or some other minor matter, and leaves me a voicemail, and I get back to them five or ten minutes later, it's not the end of the world. If your server is down, it's costing you a million dollars a minute, and you need me to remote in and fix something, well, you
really don't want me trying to
type on the freeway, as I could well mess things up even worse due to lack of focus, and then crash into something and get myself killed. Then you'd have an even bigger problem on the server, and nobody to fix it. If it's a medical emergency, what are you doing calling me, anyway? Call 911, they'll actually be able to help you.
If you need some function to be reachable 24/7, and it is truly vital, you'll have someone on duty and paid for those hours. Anything else, and you'll just have to accept that best-effort doesn't mean drop-everything-for-every-little-problem-or-question.
I'm not a call center, I'm not a robot, and I'm not the slave of anybody who can dial my digits. If the reason that you are calling is not important enough for you to leave a voicemail so that I can call you back, then that says something about how important the call was to you. If you can't be bothered to leave me a message, why should I care about what you have to say?
Now, for my friends, and people I
like to talk to, I may call back even if they don't leave a message, but I don't guarantee it. And really, how hard is it to wait for a beep and say "Hey, this is Joe, everybody's meeting at the hamburger place tonight. Call me back if you're coming."?