Mobile telecommunication networks consist of several coexisting, independent domains. Communication protocols in these diverse domains can be broadly classified into IP-based and SS7-based protocols. Modern IP-based network nodes already rely on Service-oriented Architectures (SOA) while SS7 based system is based on switching offices and a specialised service control. Service-oriented mediation between those networks is a challenging task. This paper addresses interoperable servicemediation by combining service descriptions, protocols and the integration of application data. The service mediation approach aims to combine performance-oriented interoperability with SOA concepts.