Abstract: A system and method is provided for controlling the signalling between the subscriber of a mobile station and an external service node such as a message center. The control of the signalling is carried out by using unstructured supplementary service data (USSD) which is analyzed by a USSD handler of a home location register which invokes a transparent transfer to external service node (TTEN) application when the USSD does not correspond to a service defined within the home location register. The TTEN application establishes a dialog with the subscriber of the mobile station and the desired external service node by using USSD. This allows the subscriber of the mobile station to access all message services by sending one service code. Also, the operator is not busy while accessing the services and any incoming calls may be answered while accessing the services.