said by 47717768:All it say's is "UNKNOWN NAME" "UNKOWN NUMBER" on the called ID.
Telco actually receives the calling number of every incoming call; however, if the call has the "privacy" flag set, DID residential and business service must respect it and displays whatever your provider or device uses to indicate that the number is not available to you. Note that *ALL* calls placed *to* toll-free numbers (800, 855, 866, 877, 888) provide the originating caller's number regardless of any Caller ID blocking setting the caller may have.
As to your question, some telcos (for a fee) will let you block *all* calls to you that do not provide end-point CID. Blocking individually only blocks *that* particular number, not all "Unknown" ones. Many newer phones have a feature that lets you do this (phone usually rings once, caller gets pickup followed immediately by hangup). My phone does this and also lets you use wildcards for blocking (but it only is moderately useful since the worst offenders use numbers from random NPA/NXX).