I found this link to the AMA site while looking at Sena head sets. http://www.americanmotorcyclist.com/Rights/State-Laws.aspx (http://www.americanmotorcyclist.com/Rights/State-Laws.aspx)
There are some interesting laws about helmet speakers among other things. It would be a useful reference to have on your smartphone if you were to travel cross country. The states are united, but not when income to motorcycle laws.
Even more interesting are the helmet speaker/bud rules. Some states prohibit them, some don't. IIRC, in MD, you can only have a speaker/bud on/in one ear.
In Kalifornia there is no restriction on ear plugs but only allowed one speaker/bud. Not sure what the difference is in not hearing due to ear plugs and not hearing due to music.