State bans are already occurring. Indiana just banned phones from schools a week or two ago.
A quick look at Indiana's law and the news articles are interesting. The law requires schools to implements rules that ban phone use during class, but the actual rules and implementations are left for schools to decide. The articles I found make that sound like the law is toothless and passes the hard work off to school systems, but in my opinion that's a great law as it let's every school do what works best for them without prescribing a single solution for everyone.