I think the difference is because 1) there are statistics that show the involvement of cell phones in accidents. That involvement is higher than that for other distractions:
“Virginia Tech Transportation Institute researchers and the National Highway Traffic Safety Administration (NHTSA) tracked 100 cars and their drivers for a year; they discovered that talking on cell phones caused more crashes, near-crashes and other incidents than other distractions (100-Car Naturalistic Driving Study, April 2006).”
and 2) there are scientific studies that show that talking on a cell phone is more distracting than talking to a passenger
”“Cell-phone conversations consume significantly more attention than passenger conversations, resulting in more incidents and crashes during simulated driving, Rose and Hunton concluded. “More working memory is consumed by cell-phone conversations relative to passenger conversations, and fewer resources are available for the driving task.”
The two professors specialize in studying the effects of technology on learning and awareness. Their article summarizing their research findings, “Cellular Telephones and Driving Performance: The Effects of Attentional Demands on Motor Vehicle Crash Risk,” appeared in the October 2005 issue of the journal Risk Analysis. No outside funding was received for the study, they note.”
Additional data
“University of Utah researchers determined that motorists on the blood-alcohol threshold of being legally drunk were able to drive better than sober cell phone using drivers. A key researcher and author in this field, Psychology Professor David Strayer notes, “Just like you put yourself and other people at risk when you drive drunk, you put yourself and others at risk when you use a cell phone and drive. The level of impairment is very similar.” Also, consider they found motorists to be more accident-prone and slower to react when talking on cellular telephones. It did not matter if it was hands-free either because of “inattention blindness”, a syndrome that makes a driver less able to process visual information.”
and 3) the ubiquitous use of cell phones in cars is causing the number of accidents to increase.