While the Feds have already freaked out before about it not being able easy enough to wiretap Voice over IP phone calls, there's a new trade group being formed called the VOIP Security Alliance dedicated to the opposite problem. The group, which includes companies like Siemens and Qwest (but not Vonage), was created to address "security threats" related to VoIP, but they're also concerned that "spit", or "spam over Internet telephony" (aka "vam") is going to be a huge problem once large numbers of people are using VoIP. Without some safeguards in place, the fear is that it'll be too cheap and easy for voice spammers to blast out messages to people (how long until someone figures out how to voice spam every Skype voicemail box?). Since you use an IP address to route VoIP calls instead of (or in addition to) a regular phone number, there's no technical reason why a voice spammer couldn't barrage you with pre-recorded messages at virtually no cost to them, just like they do with regular spam. A company called Qovia has already created VoIP spamming software to prove it could be done.