I do believe a hands-free cell phone option does make driving safer for someone who is talking on the phone while driving. Its certainly not the answer, as the driver is still not focused 100% on their driving. I believe it is better to leave the phone along, while in the driver's seat.
Yes, a hands-free cell phone option makes driving safer, because it lets drivers concentrate more on their driving. If a driver has their hands free, their reaction time is faster than a person who is trying to hold onto a phone. With one less distraction, a person will do a better job of focusing on their driving and the other vehicles on the road.
A hands-free cell phone makes driving a lot easier. There' no one holding onto the wheel with one hand, nor does anyone try to pick up a cell phone that might have fallen on the floor. A hands-free option isn't perfect as people can still be distracted while driving. However, it is better than the alternative.
On one hand, it is much safer, as you have both hands on the wheel, but on another, you need to be focusing completely on the road instead of what someone is saying. If you really HAVE to take a call, it would be a lot safer using a hands free device, although this is not advised.
Obviously, the safest use of a cell phone in the car is to not use one. But, since some people simply will not be that responsible, an option that keeps their hands off of it is the best we can hope for. If nothing else, it keeps the hands free and keeps the eyes away from dialing in a number or things like that. Safer, not safest.
I believe a cell phones hand-free option does make driving safer, but using a phone while driving is still distracting. My car even has built in bluetooth, but I still find talking on the phone and driving far more distracting. The person on the other end of the line is unaware of traffic issues, like a passenger would be.