I really should've read the whole thread before posting, because now I have more to say, not that anyone cares lol. The problem is that everybody breaks the law. These "upstanding scanner listeners" you speak of will, at some point, break the law. Think about it. You've done something illegal within the past week, you just most likely didn't get caught. I have met some very nice police officers in my time, but I've met some real pigs too. So has my family and many people who I trust not to tell tall tales about police misconduct.
Another problem I see is, if a person is arrested and their phone is searched, what about the other stuff on the phone. If the police are considerate, they would simply look for a scanner ap, but that's just too much to ask. If they have your private conversations in their hot little hands, and they have such an easy opportunity to catch you in more criminal activity, don't think they won't use it.
Let's take the previously mentioned highpathetical 20-year old sipping a beer at a party. If the cops get his smart phone, they could read all of his text messages including the one where he admits to smoking a joint last week. Now he can be charged with posession of a controled substance as well. If they get his laptop, they might find the songs he downloaded from that peer to peer network. Doe s he have no shame, he got them all for free! What a travesty! He can now be charged with copyright enfringement.