[Can mandate be far behind?] It would seem natural, then, to offer motorists friendly, yet stern warnings about another bad habit: holding a cell phone while driving, whether for texting or talking.

Several software and gadget companies — many of them at the country's biggest trade show for the wireless industry last week in Las Vegas — have sprung up to address that challenge. But creating an effective, widespread solution looks a lot harder than putting in reminders for seat belts.