I agree the law should attempt to be specific, but I have to point out that this is still quite ambiguous!

Is it permissible to dictate/listen to text messages on my handheld smartphone, so long as I don't hold it in my hand? Can I click "next track" on the steering wheel, but not on my phone screen?

What about smart watches? They are not handheld, but they are equally distracting, if not more so than a phone because their screens are so tiny and fiddly.