I have been involved with VoIP security for a number of years. The work was supported by two NSF funded projects which summarized below.
Project 2: This is funded by National Science Foundation. The main site at University of North Texas at Denton. A Test-bed to Study Security Issues in IP Telephony (funded by NSF) : Over the past few years, there has been rapid development and deployment of new strategic services using the IP protocol, including Voice-over-IP (VoIP), peer-to-peer, and IP-based media distribution (IPTV). These services ride on private and public IP networks and share their network with other services, such as web traffic. These new services are being aggressively deployed and it is estimated that in a few years most enterprises and residences will be transitioning from a circuit-switched to VoIP services. For example, the Department of Defense (DoD) and the Navy have announced the deployment of 400,000 and 300,000 IP phones, respectively. Similarly, Bank of America, American Airlines, and Ford Motor Company have announced plans for migration. It is envisioned that interactive multimedia and broadcast video services will be reusing the infrastructure that is being deployed for VoIP. The new services require security, robustness, and quality of service beyond those needed for email, web access and the like. Mobility adds another dimension of complexity to these new services. With the increasing penetration of the new services, the IP-based multimedia communications service will become a critical infrastructure. The goal of this infrastructure acquisition project is to create a testbed for supporting experiments that can be used for research, development and testing of inter-domain security, QoS mechanisms for new services such as voice, multimedia, and video. In addition, we plan to experiment with next-generation emergency calling for VoIP systems.