A method and apparatus for routing billing request and response messages to a billing server for serving calls by a particular subscriber. When the subscriber originates a call, an original billing request message is transmitted to an agent server. The agent server determines which billing server serves that subscriber and forwards the billing message to the selected billing server. The billing server responds to the request message with billing request data. Advantageously, this arrangement minimizes the problems of updating a large number of subscriber identification/billing server identification databases.