Voice over IP (Internet Protocol) is a technology that combines the service offering of a telephone (long distance voice transmission) with the principle of the internet and allows for computer-to-telephone, telephone-to-computer, computer-to-computer and telephone-to-telephone communication.

In case of computer based messaging, often so called Softphones, software that emulates a telephone with address book like Skype is used. For telephone-bound use-cases a more complex backend infrastructure is neccessary.

The advantages of VoIP are lower costs to companies and better programmability of internet based communication software that leads to better integration into other communication and collaboration software. The result is called unified communication.