Out all my years of driving and riding. All the close/accidents were from slower drivers and indecisive drivers. I rarely seen any close calls/accidents caused by someone going or going above the speed limit. I agree cell phones will cause more distractions, but not any more than someone putting make up on or eating a BigMac. And you really cannot inforce the laws unless cell phone makers produce phones that shut down in a moving vehicle.
There are a million things that distract drivers.