Voice over Internet Protocol (VoIP) is eroding the use of traditional wired phone service in the home and business. The market leader is tripling subscription rates in one year which will continue to rise. As with any new technology now that it is up and running concerns turn to the security of the information being transmitted. Due to the fact that VoIP networks are often implemented over the public Internet they are left open to attacks. Vinay Rao offers a well-structured and in-depth look at VoIP security with an emphasis on SIP-based applications. He will explain protocol fundamentals, review threat analysis and hardening of security. Real-world issues and countermeasures will be discussed extensively resulting in a basic security checklist on which to base future security implementation architecture schemes.