We would like to know if it is possible to reject incoming calls with unknow calling number. It is possible to reject incoming calls with known calling number, it is possible to reject it in the gateway, but is it possibel with an unknow calling number?
As long as it isn't coming in from an MGCP circuit, you can block the call with a call-block translation pattern which matches a null ANI.
Check out this link:
If you are running MGCP, I can't think of a way to do it, since CUCM can't match based on an ANI.