While this may sound good at first, I have to say this law seems to just be a law of convenience since it is easy to see if someone is using a cell phone or not. However, I feel strongly that putting on makeup, eating fast food, swapping out CDs or messing with your radio, reading a book (yes, I have seen people doing this on I-5), putting the binky back in your baby's mouth, and any number of other distractions probably contribute just as much or more to accidents than talking on your cell phone.
In addition, how are people supposed to actually place calls? There is nothing in the law that states you have to be able to dial in a hands-free mode so people will still be looking down to dial, which is probably more dangerous than actually looking at the road and talking on the phone.
As you can see in the text of the actual law (PDF document) it is a bit short on detail and looks to leave a lot of discretion up to the enforcement officer.
I think Jeremy Toeman's blog post on this issue in California does a nice job of summarizing the evidence and is what I think about the situation.
Right now, both of these laws are secondary enforcement laws so you can't be pulled over for breaking one of these alone. However, the seat belt law (another one I am not sure is warranted) started off as a secondary enforcement law and after a couple years became a primary law. I am sure in 2 to 3 years we will see one or both of these becoming primary laws too since the legislators will see that more tax revenue can be captured by making them primary. These secondary laws will help them gauge how much revenue can be generated from these laws and they will see it is another great moneymaker, whether it actually has any impact on traffic accidents or not.
I posted a review roundup of several hands-free solutions that people may be interested in checking out as they look for a good hands-free solution. I personally plan to use the new Aliph Jawbone most of the time, with the Etymotic Hf2 with my iPhone and new iPhone 3G. I make very few calls in the car, since I am a train commuter, but I do plan to keep using a wireless headset because my devices support Bluetooth and I personally prefer to have nothing restrict me while I am driving. However, I am a very cautious driver who has not received a ticket since I started driving on my 16th birthday over 20 years ago.
I may change my mind about the law if there was evidence that supports it directly, while also showing the impacts of other distractions. Will the government next ban fast food drive-thrus, kids in your car, CD players, and seats for passengers who may distract you with conversations?