Yes I mean a caller that doesn't send it's CLID, when I was in Florida if I called someone using my voipdiscount.com trunk it would show as "anonymous" or "number withheld" and some of the people I called had what AT&T called "Anonymous call reject" where it would say something like "the person you have called does not accept calls from unknown numbers, please redial and send your caller ID" and I wondered if it was something that could be done in SAIL. Also I used to install a small phone system in the UK called Jeeves and if you didn't send a valid CLID it would ask you to record your name and then when you answered the phone it would play it back for you so you could decide whether to speak to them or reject the call, the system seems to have been discontinued and I have never seen anything else like it since.
Regards,
Del