An instant messenger service system for providing an instant messenger service is disclosed. The instant messenger service system comprises at least one communication terminal for storing at least one instant messenger software, and using the instant messenger service through wired local area network communication and/or wireless local area network communication, a communication network being connected to the communication terminal, for supporting the wired local area network communication and/or the wireless local area network communication, and the Internet protocol-private branch exchange for providing the instant messenger service and a voice communication service between the communication terminals after being connected to the communication network, and providing the voice communication service by means of VoIP (Voice over Internet Protocol) technology when a request of the voice communication service is received from a specific communication terminal receiving the instant messenger service.