One of the hottest technologies these days is voice communication over packet-switched data networks. This is known as voice over Internet protocol (VoIP). Hardy (2003) defines VoIP as “the interactive voice exchange capability carried over packet switched transport employing the Internet protocol.” With VoIP, voice signal from the sender is digitized into packets that are transmitted to the receiver through a network,which often includes the Internet. As the Internet is a free resource, the communication cost of VoIP is much lower than that of traditional telephone systems. This is a major advantage of VoIP. VoIP system also increases the efficiency and service quality of businesses. As a result of VoIP, many advanced applications can be built and these include unified messaging, video conferencing, and ring list. But VoIP is not without its limitations. Its main drawback is low reliability. It also suffers from uncertain quality of voice transmission. In addition, it cannot guarantee security because it uses public networks. Although the idea of VoIP was known from the 1970s, it did not become commercially viable until 1995, when Vocaltec became the first company to produce the first commercially available VoIP product (Varshney et al., 2002).
Unified Messaging
