In a call set-up method using SIP-T overlap signaling, rather than waiting for receiving every digit of a called number dialed by a caller, when digits capable of a number translation are received, a bearer channel connection is immediately performed so that a delay in transmission of a ring back tone can be prevented. In addition, in case of using a user data protocol (UDP) within an Internet protocol network in order to connect an originating PSTN and a terminating PSTN, INVITE messages are transmitted with some time difference, which makes it difficult for the terminating PSTN to know the transmission order of destination digits. In transmitting the messages using the UDP protocol, SIP "To" header lengths of the INVITE messages are compared in order to recognize a transmission order of the dialed digits. Therefore, more effective sequence delivery can be provided.