Just like with IP proxies - it's easy to originate call from Google talk, or other free calling service to remain totally unidentified. Best way to filter call

Just like with IP proxies - it's easy to originate call from Google talk, or other free calling service to remain totally unidentified. Best way to filter calls during the meeting - don't pickup the phone and let caller to leave voicemail. At a first hint of a spammer - just block the number. Done.