said by thomas2011 :
i can not think of any practical reason why the police and/or other government officials should transmit such CID.
I've had a couple of (legit) calls from the police with a blocked caller id: the police officer was calling from home.
I route anonymous calls to a "We do not accept anonymous calls on this number" recorded message (in case they are legit), and calls with obviously fake caller id to hangup or busy.
Skype calls (when the user doesn't have Skype-in) used to produce an obviously fake caller id, but I think this has been changed. (For me, skype calls fall in the telemarketer category anyway).
I'm also considering routing all 18XX callers directly to voice mail.