A leading member of the Jericho Forum security group has criticized the security of voice over IP technology after researchers revealed that it was possible to eavesdrop on VoIP conversations.
http://news.com.com/2100-7355_3-6205178.html
http://news.zdnet.co.uk/security/0,1000000189,39288928,00.htmAlso see:

VoIP, unified communications study reveals challenges

VoIP and unified communications applications have caused performance issues with other applications as companies continue to converge communications applications onto their IP networks, according to a recent study conducted by network management supplier Network General.
http://www.computerweekly.com/Articles/2007/08/29/226429/voip-unified-communications-study-reveals-challenges.htm