From this article I understand it is not forbidden to do so while driving, in USA or in some state(don't know if it's forbidden in some state(s)
http://mashable.com/2013/04/11/texti...driving-kills/
In Sweden it is allowed to do so.
In Denmark it's forbidden and it gives you a "Cut" in your driving license if you do(if you being caught doing it)If you get 3 cuts within 3 years, you get your driving license suspended, conditional
Markus