The invention relates to a method for providing service continuity with respect to a registration of a mobile terminal, UE (1), at a control server (3) of an IP Multimedia Subsystem, IMS, network, while a CS-communication session between the UE (1) and a switching server, MSC (2), of a circuit-switched, CS, network is established. The control server (3) comprises a registration timer which is used for initiating a termination of the registration of the UE (1) at the IMS network, when the registration timer expires, wherein the control server (3) updates the registration timer in dependence of a control information received (11, 24) from the MSC (2). The invention further relates to a MSC (2) providing such service.