A Dual mode mobile terminal (MT2) comprising a WLAN interface (WLAN_NIC) and a cellular radio interface (GSM_NIC) has been described wherein when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC), indicating an incoming voice call over the cellular radio interface, or upon receiving an indication from the user of the dual mode terminal to perform an outgoing voice call, performing a determination (7) as to whether a WLAN coverage is possible from an AP providing WLAN telephony calls, and if so responding, by issuing a WLAN call message (8) to a WLAN AP over the WLAN interface to an interworking node (IWFN). There is moreover provided an Interworking node (IWFN) comprising a cellular control unit (CTRL_SIP), a cellular unit (GSM_U), a voice over IP unit (VO_IP) and a router (R), which upon receiving a WLAN call (9) from a dual mode terminal via a WLAN AP, is establishing a connection against a serving mobile switching centre (S_MSC/VLR) (10,10a, 10b), is performing a call initiation procedure (12-15), a assign traffic channel procedure (16-20) and a call confirmation and call accepted procedure (22-27) between the dual mode terminal (MT2) and the serving switching mode centre (S_MSC/VLR), is initiating duplex GSM/IP translation (29) and is routing the cellular call between the AP and the serving mobile switching centre (S_MSC).