I was just very surly to a telemarketer yesterday, and I learned something interesting as a result. I have callerID and usually simply don't answer the phone when it doesn't successfully resolve the number, but recently a new law making it illegal to hide one's number was enacted. So I answered and immediately confronted them with 'Isn't it illegal for you to be hiding your phone number from my caller ID?'
The response was 'No. But I can tell you my phone number.'
Further probing led to the revelation that she was not selling something and so was not subject to that law. In fact, she wanted to ask my husband how he felt about prescription eyewear.
'I don't think he'd be interested in that either.'
So the evil ones have already found a loop hole.
It's actually easier if their numbers don't resolve .