A study by the University of Utah reveals only 2.5 percent of people can call-and-drive with sufficient focus and safety:
The University of Utah psychology department analyzed the behavior of people while driving compared to how they are while driving and talking on a phone at the same time. According to the results, 97.5% of participants were unable to do both tasks with sufficient focus and safety. Most people were 20% slower with their brake reaction time, and the distance they kept between themselves and the car in front of them increased by 30%. The study took place with participants in a driving simulation machine instead of actually being on the road. So reaction time was down pretty much across the board...except for 2.5% of participants, which the researchers refer to as "supertalkers."