From Bill's original link, positing another variant of phreaking of converging IP phone systems:

Cooper thinks it could be taken further. He said he believes it's possible to plant a Melissa-type virus into a phone system, causing messages to be sent out to everyone else who is listed in your speed dial, or perhaps to everyone in your office. He also thinks that voicemail could be sent as a .wav attachment to your email address list.

"We have all seen the power of VBS scripts lately. A script can easily be written to exploit all of the functionality of these converging technologies."

Cooper also said he wonders if an attack could be mounted by leaving a carefully constructed voice message in someone's voicemail box, "then phreak/hacking the voicemail box to propagate the message to everyone's voicemail box in the local PBX, then have each IP phone automatically place a call to a 1-800 service number, where the message would prompt through an automated answering system -- sort of a phoneBot, you know ... 'Say or press 1' -- and essentially create a denial-of-service attack against a call center."

"Again, this is possible, but not plausible," Valiant said. "Why would you bother? No one would...."

D'uh! Ifn you have the wits to do that, all you gotta do is set up a chargeable number in say Honduras, get all the phones in the hijacked system calling it, and retire to somewhere with no extradition laws... That's the trouble with techies, no market savvy! :)