You do not always need a computer to use VoIP systems. VoIP phones are standalone devices that receive their signal from your Wi-Fi router or are plugged directly into your Internet modem. Sometimes you'll want to chain your VoIP phone through your computer to use certain computer-related features, but it's not a requirement for most VoIP phones. To use the "softphone" application some VoIP vendors offer, you will need to install it on your computer and then turn on your computer each time you need to use it.