SecureLogix and the folks at NoJitter will be releasing a "Security In Communications: Report to the Industry" next week at the Enterprise Connect conference (www.enterpriseconnect.com). This report discusses voice/communications security, which threats are the most severe, why these threats are here now and why they will get worse, and then threat data from real-world assessments and deployments.
For a glimse of what is in the report, take a look at the summary posted on the NoJitter site:
http://www.nojitter.com/feature/229219335