It has always been legal to listen into radio communications. But you can't repeat what you heard. There was an exception with the Communications Act of 1987 which stated that you could not listen to the 806 to 960 MHz. frequencies used in 1st gen. CEL communications. It never covered PCS or AWS bands. Back then I think it was to remove "wiretapping" by the police. Buy a current radio scanner, it won't let you listen to those frequencies. Sort of a moot point now with 3rd and 4th gen. digital communications. If I can't repeat what I heard on the scanner, how can wi-fi snoopers?
Here, the law is a scanner is only illegal to own if you use it for illegal activities. It is not against the law just to own it. Even had the police chief agree with me at a crime watch meeting last year about this.