Internet telephone services like Skype and Vonage are starting to look less like digital gimmicks and more like the next generation of voice communication. They’re cheaper than traditional phone services and increasingly fast and reliable. But they may also be far more hackable.Security professionals at the Black Hat conference in Las Vegas spent Wednesday outlining the exploitable vulnerabilities in voice over Internet protocol technology, or VoIP. In a series of presentations, they demonstrated ways in which cybercriminals can eavesdrop on VoIP calls, steal data from Internet telephony devices, intercept credit card numbers from VoIP connections and shut connections down altogether.”VoIP is about convergence. The idea is that you save money and resources and time,” said Barrie Dempster, a senior security consultant at Next Generation Security Software who made a presentation at the conference. “But convergent systems give you more avenues of attack, more ways in. It’s not a secure environment.”
http://www.forbes.com/technology/2007/08/02/voip-security-flaws-tech-internet-cx_ag_0802techvoip.html