Making a phone call is one thing, in the early days of mobile phones I would take and make calls behind the wheel (prior to that it was the CB radio!). Today they are sending and receiving texts, using Facebook and Twitter and trawling the net.
Using a Sat Nav on the move is just as bad, as is an iPod.
Just to make it clear, I think any mobile phone use, while driving, is dangerous and stupid, even hands free. When I am out out on the van I do not answer my phone, but find a safe and suitable place to stop before calling the depot back. They know and fully endorse that. My employer, TMS Motor Spares, is a very safety conscious organisation.