For a legal classification of Voice over IP, several aspects have to be taken into consideration. Where regulation focuses on technology - and there on the regulation of voice telephony - the definition of voice telephony is the starting point for all further legal and practical considerations. But when it comes to Voice over IP, terminology is used quite inconsistently. The lack of a clear definition often leads to misunderstandings and also problems in the exact legal classification.

Internet telephony (or Voice over IP, VoIP) can be defined as a collection of Internet applications for real time voice traffic over data networks using the internet protocol (IP) whereby the quality of the transmitted voice depends on various factors such as available network capacity, gateways, and audio codecs used, etc.

For Oftel, "Voice over Internet Protocol (VoIP) is the generic name for the transport of voice traffic using Internet Protocol (IP) technology. The VoIP traffic can be carried on a private managed network or the public Internet or a combination of both. A wide range of applications and services could use VoIP technology, from traditional telephone services to interactive games." "Internet telephony" (also referred to as Voice over the Internet) - according to Oftel - "is a specific type of VoIP service that uses the public Internet to carry the IP traffic."^[4]

The ITU^[5] uses different definitions depending on the nature of the principle underlying the means of transmission. Therefore, Internet Protocol (IP) Telephony is the transmission of voice, fax and related services over packet switched IP-based networks. Internet Telephony and VoIP are - according to the ITU - specific sub-sets of IP Telephony. Internet Telephony therefore is IP Telephony in which the principal transmission network is the public Internet. Internet Telephony is also commonly referred to as "Voice-on-the-Net" (VON), "Internet Phone," and "Net Telephony" - with appropriate modifications to refer to fax as well, such as "Internet Fax". Voice-over-IP (VoIP) then is IP Telephony, in which the principal transmission network or networks are private, managed IP-based networks (of any type).