The way that the separations of powers work in the US, basically all driving laws are set by the states. The rules for driving can and do change when you cross state lines in the US, sometimes significantly. It really doesn't make any sense to talk about specific driving laws in the US as a monolith.
Same here in Australia. I actually think we have developed the technology (and the matching legislation) that allows pole mounted cameras to detect this while driving at 110kmh down the expressway. I know many people that have been "busted" and even though I use a handsfree holder, just placing (when you forgot to do so before you drive off) is just as illegal here.
I did laugh when of course sometimes they would pickup someone holding a chocolate bar while driving. While not necessarily the best thing to do with the one hand, not illegal all the same.
The way that the separations of powers work in the US, basically all driving laws are set by the states. The rules for driving can and do change when you cross state lines in the US, sometimes significantly. It really doesn't make any sense to talk about specific driving laws in the US as a monolith.