On a related note, it's possible Tracfone's prepaid calling cards have been the target of fraud. This post claims people are selling Tracfone cards on eBay, and references this thread as "proof". I also found a site which teaches ways to defraud Tracfone, complaining that Tracfone defrauds its customers.
Let me make it clear that none of this discussion is intended to assist the reader with defrauding anyone. I try to understand these techniques because my professional career involves helping companies to combat fraud.