Using a known Intelligent Network Architecture a service invocation message is addressed via a Sorter to an appropriate Server. After interrogating the caller when necessary, the Server may re-address the message directly to another Server within the same organisation or consortium, which may in turn repeat the process. Thereby a Service Provider representing a large business organisation or consortium offers a single umbrella service and is able to introduce new services or sources of information, and to cease, re-configure or resituate the existing services with no effect whatever upon public network or message network equipment.