
Voice over IP (VoIP) spam - also amusingly known as Spam over Internet Telephony (SPIT) - is largely a theoretical problem at present. As with all communications media, VoIP may well be used for unsolicited bulk communications once it comes into wider use.
VoIP spam - en.wikipedia.org/wiki/VoIP_spam
VoIP Security Alliance - www.voipsa.org/
SIPassure - www.borderware.com/products/sipassure/
SPam over Internet Telephony threat grows - www.voip-news.co.uk/2007/11/01/spam-over-internet-telephony-threat-grows/