Both DUI and Cellphone use (non-handsfree) are illegal in California.
There are different studies that have been done on how talking on a cellphone affects driving. On July 1, new laws go into effect in California that prohibit motorists from holding a cellphone and driving -- in other words, they have to use hands-free devices.
Dave Strayer, a professor of psychology at the University of Utah, has been part of a team of researchers who over the last several years has published several studies on the topic and tested how cellphones affect motorists using a driving simulator.
Maybe this quote from Strayer on a recent university press release gives you a hint of how he feels:
"At the end of the day, the average person's commute is longer because of that person who is on the cellphone right in front of them. That SOB on the cellphone is slowing you down and making you late."
Strayer believes that it's the conversation, not the device that is diverting the attention of motorists from the road. He said that hands-free laws are not based on good science.
"It’s also possible [such laws] can be sending another message to people that we’ve solved the problem, and technology has come to the rescue," Strayer said. "If it encourages people to talk when they otherwise [would] not talk, it could be counterproductive and make roads less safe."
Using the driving simulator, his team concluded that people talking on a hands-free phone while driving pretty much drive as if they were drunk and they drive slower than the traffic around them. In particular, motorists engaged in phone conversations were less likely to change lanes and tended not to pass slow traffic in front of them.
Oher distractions that motorists face: people eating greasy French fries, playing with their iPod or screaming at their kids etc. The difference is that those types of distractions tend to be ephemeral and pass quickly, whereas cellphone conversations can last a long time.
Legislators in most states have shied away from passing cellphone driving laws, and no state has passed a law saying you can’t talk on a cellphone at all. Change may ultimately come about because of pressure from the insurance industry or from large employers, who worry about being responsible if one of their employees gets involved in a cell phone-driving accident.