stox writes "As many of you know, AT&T has implemented caps on DSL usage. When this was implemented, I started getting emails letting me know my usage as likely to exceed the cap. After consulting their Internet Usage web page, I felt the numbers just weren't right. With the help of Tomato on my router, I started measuring my usage, and ended up with numbers substantially below what AT&T was reporting on a day-to-day basis. Typically around 20-30% less. By the way, this usage is the sum of inbound and outbound. At this point, I decided to contact AT&T support to determine what exactly they were defining as usage, as their web pages never really define it. Boy, did I get a surprise. After several calls, they finally told me they consider the methodology by which they calculate bandwidth usage to be proprietary. Yes, you read that right; it's a secret. They left me with the option to contact their executive offices via snail mail. Email was not an option. So, I bring my questions to you, all-knowing Slashdotters: are there any laws that require AT&T to divulge how they are calculating data usage? Should I contact my state's commerce commission or the FCC to attempt to get an answer to this?"