It is the business practice of sending all clients' billing info to a separate company, who then does everything for you. It also allows a company to cut down on time and human resources spent on administrative tasks.
Rates of the call shop are usually defined by the administrator, but the rate plans are managed in the main database of the billing system. All the rates are dependent on the charging policy; in case of a destination based billing rates are specified according to the area codes in the supported destinations.