A VoIP Privacy Mechanism and its Application in VoIP Peering for Voice   Service Provider Topology and Identity Hiding
  Voice Service Providers (VSPs) participating in VoIP peering frequently want to withhold their identity and related privacy-sensitive information from other parties during the VoIP communication. A number of existing documents on VoIP privacy exist, but most of them focus on end user privacy. By summarizing and extending existing work, we present a unified privacy mechanism for both VoIP users and service providers. We also show a case study on how VSPs can use this mechanism for identity and topology hiding in VoIP peering. 
Charles Shen and Henning Schulzrinne