A method of providing in a packet switched telecommunications network, for a communications session involving a user of said packet switched telecommunications network a value added service associated with a circuit switched telecommunication network. The method comprises the steps of establishing a first signaling data stream of a first basic call state model of a packet switched dedicated protocol type between the packet switched telecommunications network and a service interface adapter unit, and establishing a second signaling data stream of a second basic call state model of a circuit switched dedicated protocol type between the service interface adapter unit and the circuit switched telecommunications network, based on information from the first signaling data stream, for providing the value added service from the circuit switched telecommunications network. The information is augmented with further information for establishing the second signaling data stream, and for exchanging data between the first and second signaling data stream for providing the value added service to the user through the packet switched telecommunications network.