A method and device for initiation a mobile originating service-based inter-system handover. At least two radio access networks (RANs) of different types, i.e. RAN of a first type and a RAN of a second type. A dual-mode mobile terminal communicates with the communication system via the RAN of the first type. The initiation of the inter-system handover is included in a transmission including a bearer capability (BC) field. The BC field indicates that a requested service is only operable with the RAN of the second type. In particular, at least one BC field is set to a parameter value, which serves as indication for the receiving network and its processing entities, respectively, which receiving network indicated to carry out the inter-system handover initiated by the mobile terminal.