Just curious how easy or hard it would be to write say, two simple scripts,
 
script one, which would be called when a user dials, say, *60
have an audio prompt say, press 1 to add a number, 2 to remove
a number, 3 to list blocked numbers and so forth.
 
When they add or remove a number, it would add say
callers_extension:number_to_be_blocked
 
Now, on to the second script. When we get an incoming call from the pstn/sip trunk
to the above persons number, it looks at the list. If there is a match between the
destination and the callers number, we play a message saying that their call is not
being accepted and hangup, else do nothing and pass the call through.