The Docs given the best advice, however I don't see the need for people to use mobile phones at all whilst driving unless there is an emergency and you follow the procedure and pull over. There are many well documented cases of fatalities caused through silly little girls and boys texting and using mobiles whilst driving that have left families devastated, is it worth it for the sake of a phone call?
There is a need of course particularly if you are in business. It can save hours if you are needed somewhere close to where you have just been if you are on your way back. However I have no truck with anybody if they do not have total hands free. Cars today have built in 'bluetooth' where you actually speak to your car and never need touch your phone at all. If a business person cannot find a suitable car then you can have your phone built in for £275 + VAT (that was the cost when I was in business before 'bluetooth' cars so it might have gone up)This should be considered an essential business expense and can be set against your tax bill, so again there is absolutely no excuse and it is highly dangerous to do otherwise.
BTW My 'Mazda 3 TS2' has built in Bluetooth and is a super car as well, I thoroughly recommend it.