Voice over Internet Protocol (VoIP) allows one to communicate verbally over a TCP/IP network instead of using traditional telephony methods. It has become an attractive communication mechanism for consumers globally. And with the declining costs in global communications and the brisk uptake of Internet based technology, VoIP usage will gain popularity in the years to come. However, like any new technology, VoIP has its associated positives and negatives. In this paper, some commonly used VoIP CODECs are implemented on a test-bed setup with different operating systems (Windows Vista, 7 and Server 2008) and performance related metrics like throughout, jitter and latency are measured in various scenarios. The results obtained show throughput values vary significantly between some of the CODECs while delay and jitter also vary between operating systems and versions of the Internet Protocol.