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.