As its name implies, it is a piece of software, or part of a VoIP software, that acts as an interface allowing you to dial numbers and carry out other phone functions using a screen, mouse, keyboard or keypad.

Commonly, the interface resembles a phone with buttons representing the keys, which you press using the mouse to dial.

For speaking and listening, a headset and microphone suffice. You can also use an IP phone or handset, if you have one.