Well....the main problem with that is unless you know the numbers you want to block, you can't block them specifically. There are a couple things you can try though....either set your phones ringone for unknown callers to silent, but that may make you miss some you want. Another thing you could do is to break down and purchase a PhoneAlawm type of app and set up a profile for night, silencing unknown calls. I am attatching a link to a free callfirewall app from XDA Developers. You can give it a try, but unfortunalely it does boil down to you needing the numbers to block further calls from them!!!
Good luck....I know how frustrating telemarketers can be!!!!!!
http://forum.xda-developers.com/showthread.php?t=307178
Direct site:
http://www.logic-unlimited.com/callfirewall.php
Just for kicks, I attatched the CAB as well....good luck again!!!!