Thanks to Mark Collier's VoIP Security Blog I point you to this article that Toll fraud can put SMEs out of business in minutes.
Unfortunately the premise and conclusions are correct. If you think of the example from the 2011 Astricon where a company was hit for $400,000 in fraud over 2 days then it is easy to see how this kind of hit could cost a small business everything in almost no time.
Real time monitory and proper security checks are needed to help prevent this kind of fraud. I will keep posting details on how you can protect your company, or you can contact me directly for more information about real-time monitoring or VoIP Security Audits.