The idea behind the this paper is to do a thorough overview of VoIP technology and to show what everything from the hardware, network services and protocols is needed to successfully implement the technology in a business environment. The basis for using this technology is a TCP / IP suite of protocols, without which it is not possible to successfully organize VoIP processes with a particular business entity. Therefore, this paper is intended as a kind of manual for anyone who would like to become familiar with VoIP technology. The paper provides a historical overview of the technology development in question with links that, at first glance, do not belong to them, but greatly contribute to understanding why some things are the way they are. In addition, the paper gives an overview of the most important VoIP protocols, explaining their interaction with individual protocols from the TCP / IP protocol suite, which is crucial for the quality implementation of VoIP communication system in a business communications network of a business entity. A review of the hardware that needs to equip the communication system to operate in both a local-area communications network and a global communications network, the Internet, is also given. All this is substantiated by textual and graphic explanations of the practical application of the virtual but realistically presented business organization.