A network function operable in a communication network, in which the network function is configured to receive a call setup request from an emergency service to set up a call between the emergency service and a user terminal, the received call setup request comprising a called party identifier. The network function determines whether the called party identifier is of a first type or of a second, different type, wherein the first type of called party identifier comprises a dialable number temporarily associated with the user terminal for use in receiving a call from the emergency service. In response to determining that the called party identifier is of the first type, the network function transmits priority indication data to a further network function in the communication network in order to cause the further network function to prioritize handling of the call between the emergency service and the user terminal.