Ever since the first release of ”IPhone 1.0” from the VocalTec, an Israel software company, in 1995, VoIP technology was continuingly developed. Now, with the Internet access bandwidth be improved and related issues be conquered, IP telecommunication would become more mature to be the basic service for the internet service provider. ICL has been involved in the telecommunication technology for years, as well continuingly accumulating the deployment experience. The goal of this article is to help upgrade an enterprise VoIP system to the Carrier-Grade IP telecommunication system. In this article, the fundamental VoIP technology would be introduced first, following with the system service component, deployment architecture, and related technologies. Finally, out of our experimental experience, we analyze how to improve the existing VoIP system toward a carrier-grade IP telecommunication system.