In some communications we refer to a "billing telephone number (BTN)." If you have CenturyLink internet service only, this may seem confusing, as the BTN is not a typical phone number that you can call. It is simply the number that is associated with your internet line. If you have home phone service, the BTN will be the same as your working phone number.
In essence, BTN and the term "billing account number" (BAN) are all interchangeable and serve as the account number linked to your CenturyLink service.