Hands free devices are just as much of a distraction as it is to talk on the cell phone itself. Due to the way the human brain is wired, after gaining experience, driving begins to become 'routine.' This turns into a false sense of security, however, and people think that they can do whatever they want while they drive.
In reality, however, 100 percent of the operator's focus is needed to be able to drive effectively, efficiently, and most importantly, safely. Too many variables exist when you are out on the road.
Driving is a task that requires the human brain to process massive amounts of visual information. It also requires a person to make decisions based on predictions made of other drivers as well as to coordinate precise movements with their hands and feet to make the vehicle respond in an appropriate way to the current situation.
So everyone can say that driving with a hands free device is better than a cellphone (which it may in fact be), but the truth is that better or not it's still a distraction.
When you multitask, your brain splits priorities between talking on the phone and driving. It cannot completely focus on one or the other.
What are your priorities? Is it really worth it to make a call and risk everyone in your vehicle, everyone around you, and yourself in potential danger.