Abstract: A public telecommunications system includes a local exchange 10, an element manger 11 for managing the exchange 10 and a configuration manager 12 for managing the element manager 11. The element manager 11 is located with the exchange 10 and the configuration manger 12 is situated at a distant location. The exchange 10, element manager 11 and configuration manager 12 are connected by communication links 18, 19. In order to provide a new or existing customer with basic telephony services or one or more supplementary services such as call forwarding, the configuration manager 12 sends an appropriate set of requests to the element manager 11. If one or more of the requests are not successfully performed in the element manager 11, the configuration manger 12 sends further requests to the element manager 11 to cancel the requests which have been successfully performed and thereby return the element manager 11 to its original configuration.