Service resource items (49) for use in call setup in a telephone system are held on servers (58) that are connected to a computer network which is logically distinct from the telephone system infrastructure, this computer network may, for example, make use of the Internet. Each service resource item (49) is locatable on the network at a corresponding URI and is associated with a particular telephone number. A mapping is provided between telephone numbers and the URIs of associated service resource items. When it is desired to access a service resource item (49) associated with a particular telephone number, this mapping is used to retrieve the corresponding URI (step 55) which is then used to access the desired service resource item (56, 57, 59).