Sign up for a course with the Institute of Advanced Motorists. They teach driving the way the Police and Military are taught. The driver will then understand the inherent dangers of both your stated problems. Local branches of the IAM are easy to find (check your local library for starters). The foregoing is not a deterrent but rather a positive action for practical road safety - a "skill for life".
All new cars should have a gadget which blocks the signal (they have them in some cinemas apparently). It would mean that passengers couldn't use them either, but that is preferable to the accidents caused by idiots using their phones.