A method of providing a circuit-switched, CS, service to a User Equipment, UE, over an SAE core network (11) and an LTE radio access network (12), said method comprising the steps of: extending an SGs interface to provide an SGs+ interface between a Mobility Management Entity, MME, in the SAE core network and a Mobile Switching Center Server, MSC-S, wherein the SGs+ interface supports transmission of upper layer packet data units; transferring CS service messages in SGs+ messages sent between the MSC-S and the MME utilizing the SGs+ interface, wherein the step of transferring CS service messages includes sending from the MSC-S to the MME, an SGs+ downlink data transfer message including upper layer packet data units destined for a terminating UE, or sending from the MME to the MSC-S, an SGs+ uplink data transfer message including upper layer packet data units originated by an originating UE; and transferring CS service message contents between the MME and the UE via the LTE radio access network in non access stratum, NAS, messages, wherein the CS service is a Short Message Service, SMS, and the step of transferring CS service messages includes sending from the MSC-S to the MME, an SGs+ downlink data transfer message, said SGs+ downlink data transfer message including SMS message content destined for the terminating UE. According to said method a system for providing a circuit-switched, CS, service to a User Equipment and an apparatus in a Mobility Management Entity are specified.