A method and apparatus is provided that improves the quality of voice calls in a mobile communication network. The method of performing transmission/reception of signals in an evolved Node B (eNB) of a mobile communication system includes: receiving a first message including service request information from user equipment (UE); transmitting a second message including the service request information to an Mobility Management Entity (MME); receiving a third message including context information for the UE from the MME; and determining an inactivity timer value for the UE based on the context information. The method and apparatus can maintain, when a voice call is created, connection with calling UE from when the called UE answers the call until the call is set up, thereby preventing part of a caller's voice data from being lost.