U. S. National Safety Council compiled 30 studies and concluded that it's not the hands-free phone that's the problem, it's the call. While the hands-free devices may be legal, it is still not safe to use such devices while driving.

The NSC study found that the brain doesn't do two things at once and hence multi tasking is not possible. It performs one task at a time, rapidly switching back and forth between them. This switching back and forth between tasks also results in longer reaction time.

Attending a phone call and driving on the road are altogether different things, which may result in inattention blindness. It is a situation when even though the driver is looking at red lights, pedestrians and other vehicles, but isn't able to see them.

The study also found that drivers on cellphones still make more driving errors as compared to those talking to their passengers. It is also discovered that drivers listening to the radio have better response times than cellphone talkers. This made the researchers conclude that that it's the voice communication that takes the driver's attention off the road.