I use to be able to listen to cell phones and hearing the cops or the ambulance was priceless. I also decoded pager transmissions. Yes, they still use pagers.
As far as encryption goes, ADP or DES- OFB can be broken, but AES can't. I want to developa program for SDR that can brute force the key. But then you have over the air rekeying involved so if you do manage to find the key you must progarm it into a /\/\otorola radio right away to follow rekeying. Clone the radio to the dispatcher and badda bing! Can't take you off the system. What I mention here is highly illegal. Will I develop an app to brute force a key? IDK.