I drove for about 23 years and have spent the last 6 as a clerk.
Here in California, it's legal to talk on a cell phone while your driving without a hands free device. That will hopefully end next year, I believe.
I am waiting for the fateful day when a ???pound UPS vehicle gets involved in a serious accident. I hope, for the drivers sake, that they were answering a UPS call that they were instructed that they had to take "or else". If you're on a personal cal, which I see MANY of our drivers doing, not only will YOU be toast, but somebody will own the company. That's the point that UPS will declare that no more cell calls will be made.
In our center we have mostly manual transmissions and it's amazing to me to see a driver with a cell phone stuck to their ear, shifting and steering at the same time. That should actually take 3 hands, not 2 and a knee.
I remember a short while back that a sign was posted at work that cell phones were not to be used in vehicles. I don't know what ever happened to that sign.
Also, it will be very easy for the company to say that they never instructed you to answer your cell phone while you were driving. They will say the you should pull off the road and be safe. That, of course, will be after they chastise you for not answering your phone. It's always YOUR call to answer the phone or not.
If it were me, and they had my cell number, I would check caller ID and make my call to them from a customers phone. If they don't like it, pay my bill.
One last thing, supervisors at my center got UPS issued phones for company use. A couple opted for Nextel type phones. I don't have an immediate problem with most of my supervisors as I've worked with most of them for almost all of my 29 years and we have a mutual respect for each others jobs. It's transplants above them I have the most problems with.