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.