A method of establishing a WLAN link between portable terminals using a cellular network and a sound, the method including: transmitting a connection request message including a first partial security key being a portion of a first security key to a second portable terminal through a cellular network by a first portable terminal; outputting a sound including a second partial security key being a remaining portion of the first security key after transmitting the connection request message; receiving a request of a WLAN connection including a second security key from the second portable terminal having received the sound through a WLAN; and establishing the WLAN link with the second portable terminal when the second security key corresponds to the first security key.