Voice over IP technology enabled the growth of Internet telephony applications that make use of public common infrastructures to provide voice and data communications to their users. The growth of wireless Internet enables users to connect to the network from different locations using mobile Internet devices. Security is a major concern for mobile Internet telephony users, yet the lack of secure inline key exchange mechanisms is one of the major drawbacks for the use of these applications for

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... siness use. The intrinsic vulnerabilities of wireless networks make the VoWiFI case even worse while compromising security of a call is as easy as breaching human administration security of the service network. In this paper we describe the design and implementation of a secure VoIP application for handheld devices that is using the strong security mechanisms of Voice Interactive Personalized Security protocol (VIPSec). We analyze the architectural fundamentals and we present the implementation elements of the application. User sign-in and other subsidiary procedures follow the Client-Server model while the media path is direct between the users. The application is developed in Java and is suitable for mobile devices running Windows CE or Linux, essentially securing end-to-end voice, video and data communications in wireless communications. Keywords VoIP applications, mobile devices, personal communications, privacy addresses system implementation issues, taking into consideration the necessary optimization due to the nature of the mobile devices; performance of the mobile client application is examined Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.