Interesting Cnet article which talks about an alliance being formed by VoIP service providers called "VoIP Security Alliance" which aims to prevent VoIP spam, SPIT (spam over Internet telephony) or whatever you want to call it.
What's interesting is this quote, "With little evidence to suggest a problem, however, the 22 member companies of the VoIP Security Alliance run the risk of provoking the digital world's black hats."
Hate to break it to ya, but if black hats or spammers can make a buck via VoIP spam, then they're going to do it regardless of an organization/alliance being formed.
The almighty dollar and greed will drive VoIP spam.  Still, I do agree that this may be a case of crying wolf before the wolf has actually left its cage.  But everyone seems to be prognasticating VoIP spam will happen one day, so I suppose it's better to get the best minds in VoIP together and figure out what to do before it happens.
Now if only the SMTP designers better thought out the potential for email spam... Then life would have been good...
Alliance wants to beat spam to Net phones | CNET News.com