1. A method for detaching a user equipment (UE) from a evolved packet system (EPS) network only when the UE is registered in the EPS network and a circuit switched (CS) network, comprising: sending, by the UE, a detach request to a mobility management entity (MME), wherein the detach request includes a detach type indicating EPS detach only; receiving, by the UE, a message from the MME through an evolved NodeB (eNodeB) to instruct the UE to select a CS cell; and selecting, by the UE, the CS cell.