Driving with earbuds, is it illegal or not?

This morning I was telling a story about having to pass a cop on the highway that was going slightly below the speed limit. I mentioned how I kept my hands at 10 and 2 and how I also popped my earbuds out before I got next to him. Klinger chimed in and asked, "Why? Is it illegal?"

Listener Jason sent us this handy map that shows which states it is legal and illegal to drive with earbuds in: