What are the laws in each US state on driving while cellphoning?

California will soon enact new legislation around the use of cellphones while driving. Chris Petrell says,
A couple of friends and I were talking recently about cell laws coming up. I know California is about to start requiring hands free devices, but we were unsure about Nevada. So I asked our local sheriff and they did not know off hand, so I looked online.

Here are a few web sites that talk about cellular laws while driving. I don't know how they propose to ban things like the Nextel PTT button, as you have to physically push a button to talk.

Link 1, Link 2.