Any type of phone should not be used in a car unless absolutely necessary. And if at all possible you should pull over to use the phone. You are distracted when you are having an on-going conversation with someone on a phone while driving whether you have to hold the phone or not.
Hands-free mobile phones are not just as dangerous as handheld phones, simply by virtue of the added benefit of another hand on the wheel (or shifter, or air conditioning, or radio, etc). Removing a hand from the wheel to hold a phone reduces the capabilities of a driver to interact with their vehicle and to respond to events or hazards around them. Hands-free phones, while not cutting down on the split attention issue present when trying to do anything while speaking on the phone, do allow a driver to potentially drive as they would were they not on a call, if need be. The additional available hand makes all the difference when evaluating whether hands-free is just as dangerous as handheld phones in a car.