1. A method for an apparatus of a telecommunications system, the method comprising: receiving, in the apparatus, a communication establishment request relating to a service to be invoked between a sender of the request and a recipient to whom the request is targeted, the request containing information on the sender of the request and information on the recipient, the information being used for routing the request, the sender's operator using a first service identifier for the service, the recipient's operator using a second service identifier for the service; checking, by the apparatus, whether or not the request further contains the first service identifier identifying the service to be invoked; in response to the request containing a first service identifier indicating the service, the method further comprises: obtaining, by the apparatus, interconnection information on the service, the interconnection information indicating allowability of the service between different operators, and associating in the interconnection information the first service identifier and the second service identifier with the service; determining, by the apparatus, on the basis of the interconnection information and taking into account at least the sender's operator, whether to reject or forward the request; and if the communication request is not rejected, then replacing the first service identifier in the request with the second service identifier and forwarding the request.