Voice over IP allows traditional voice/audio information to be sent over an IP network. This can often be cheaper than switching calls through the Public Switched Telephone Network (PSTN).

For example, a company with an office in Vancouver, Canada may have an American presence in Orlando, Florida. The two sites have a leased line between them that allows both sites to access the corporate network, data etc. With the addition of some kind of Voice over IP interface at both sites, telephone calls between the two sides could be made for free - the voice traffic travelling over the existing (fixed cost) leased line, as opposed to being charged by the minute for a long distance telephone call.