Maybe I'm too cynical, but I don't think it's about safety or distraction or good driving. It's all about money. Cell phone carriers have lobbied state legislatures for years to allow phone usage in cars, because it's more money for them, Just like the manufacturers of those impossibly bright auto headlights, which were at first illegal, then all of a sudden became not only legal but the new big thing.
As to enforcement, when the first offense is a fine of five or ten bucks, nobody really cares. As Glider suggests, make it a grand or so, and two things happen. First, people take it seriously, and second, the police would feel it's worthwhile to pull someone over.
By the way, if this all seems a bit rant-y, maybe it's because I got seriously cut off by a driver on his phone, today.
Ok, rant over. Happy me again.