The present invention discloses a method of interworking between different radio access networks. A radio transceiver device is capable of operating with the first radio access network and the second radio access network is attached to the first radio access network. The method comprises the steps of detecting a service request is requested. Information is accessed on conditions for the first and the second radio access network for giving sufficient support for a service requested by the service request. It is analyzed whether or not the first radio access network and the second radio access network meets the conditions, and a handover of the radio transceiver device from the first radio access network to the second radio access network is initiated if the second radio access network meets the conditions but the first radio access network does not. Thus, the present invention serves to support dual mode mobile stations and networks in such a way that the correct radio access which sufficiently supports a requested service is automatically obtained.