Evolution of the Internet and the wide growth of computer networks have made the Internet part of our everyday life. This accounts for the reason why the interest and demand on different internet-based applications has increased Steinmetz & Wehrle (2005). Voice over Internet Protocol (VoIP) technology has become a potential alternative to and supplement of the traditional telephony systems over the Public Switched Telephone Network (PSTN), providing a versatile, flexible and cost-effective solution to speech communications. Goode (2002). Koforidua Technical University spends a large chunk of its revenue on public switched network telephone. Since there is an already existing wireless network supporting file transfers, streaming and other functionalities, it would be cheaper to incorporate VoIP that could enable students and administrators communicate at a low cost. In this paper, we use OPNET modeler to simulate the effects of VoIP on a wireless network infrastructure. The simulation results obtained showed that implementing VoIP over and existing wireless network infrastructure does not have any negative effect on the system.