There have been quite a few successful prosecutions here in the UK where use of a mobile phone has been proved to be the cause of an 'accident' - sometimes with fatal consequences, and sometimes where the guilty party was sending a text message...

Mind you, I'm just as concerned by people who seem to be incapable of chatting with their passenger unless they are staring at them instead of the road. I usually beep and flash my headlights if I'm behind them (as long as there's nothing in front of them)... okay, they usually can't understand why, but at least it interrupts their conversation for a few seconds!