voip spam

VoIP spam or what is commonly referred to as "SPIT" (Spam over Internet Telephony) has been discussed extensively in the press but the problem appears completely contained. If you do a search on Google for "VoIP spam", all of the top ranked articles are of 2004 vintage. Is it simply that there is far greater economic incentive for a spammer to spend a few seconds to spam millions of people using email than to waste several seconds to annoy just one person using VoIP? If that is the case, voice communications has inherent anti-spamming characteristics.