Patent ID: 8050658

Claim:
A method for establishing a voice call between two networks of a mobile communication system via a server connected to the two networks, comprising: performing by the server an One Time Password (OTP) authentication of an origination terminal by performing a call connection between the origination terminal and an origination side network, the origination terminal transmitting a corresponding message including a first OTP key value to the origination side network; requesting by the server a call connection to a termination side network by transmitting an OTP authentication result of the origination terminal; performing by the server an OTP authentication of a destination terminal by performing a call connection between the termination side network and the destination terminal when the origination terminal is successfully authenticated, a destination terminal transmitting a corresponding message including a second OTP key value to a destination side network; establishing by the server a call connection link between the origination terminal and the destination terminal when the destination terminal is successfully authenticated; and displaying an icon indicating the OTP-authenticated call on a screen of both the origination terminal display and the destination terminal display when the call connection link is established, wherein the first OTP key value is different from the second OTP key value.