By the way, did you know you can actually screen the blocked calls and send them somewhere special...mine go to a recording that says "I'm sorry, I don't accept calls with blocked caller ID".
If you're using DIDs, either SIP or PRI, here's a cool trick: Create a new Call Routing Table and set it to use CALL ROUTING KEY: OUTSIDE PART NUMBER (CRT list page) and for description call it BLOCKED. Within that table set the first pattern to +, don't enter description, set destination type Call Routing Table and set Ring-In Destination to the number of your regular CRT. Set the next pattern to E (empty), name it BLOCKED, and set other parameters same as one above. Change the ring in destination of your trunk or SIP group to this new CRT. Now call comes in and hits this group first...if it sees a number it falls into the + bucket and goes to main CRT. If no number it names it BLOCKED and sends to main table. You can add other caller IDs in this table such as known telemarketers, as long as they're above the + and E, and send to announcement or busy ext.