SANS Whitepaper – Security Considerations for Voice over Wi-Fi (VoWifi) Systems

SANS Whitepaper – Security Issues and Countermeasure for VoIP

Department of Homeland Security – Voice Over IP

Federal Communications Commission – Voice Over Internet Protocol (VoIP) – Federal Communications Commission

TMC Net – VoIP Security Monitoring and Management; What Every Security Professional Needs to Know

NIST SP 800-53: SC-19 Voice Over Internet Protocol