A wireless communication system for interconnecting an ad-hoc network and an IS network, and a wireless terminal and communication method therefor are disclosed. The communication method includes transmitting a discovery signal including terminal information of the wireless terminal to a radio network, receiving a response signal including information for network access from a base station or another wireless terminal, which has received the discovery signal, selecting an operation mode for access to a network through the base station or the other wireless terminal, based on the response signal, communicating with the base station and accessing the IS network when the selected operation mode corresponds to a first mode and accessing a network, to which the other wireless terminal belongs, through a licensed frequency band of the IS network when the selected operation mode corresponds to a second mode. Accordingly, it is possible to support communication through an existing infrastructure and support communication of an ad-hoc network scheme, through use of a licensed frequency band assigned to the provider of an existing IS network.