Voice over Internet Protocol is a technology that allows voice traffic to be transmitted over a data network. Using a broadband Internet connection and subscribing to a VoIP provider such as Pulse VoIP allows a person to make and receive phone calls over the Internet. IP-PBX is a PBX that switches calls between a traditional telephone user or between two traditional telephone users in the same way that a conventional PBX does but has the capabilities to switch calls over IP or VoIP,

Voice is converted by a device from an analog signal to a digital signal and is then sent over the Internet where it will be converted back to an analog signal for the remaining distance over a traditional circuit switch (PSTN).
The computer does not have to be turned on, for your VoIP phone to work, as your VoIP phone will be plugged directly into the router. If however you are using a softphone, the computer will have to be switched on.

There are several advantages to VoIP over a traditional phone service, such as, price, portability, and extra features. Telappliant offer call packages that allow inclusive minutes for calls to selected destinations at one low monthly fee. A person can pick a number, rather than be locked into certain area codes and prefixes. Many features are offered as part of the basic monthly fee, such as call waiting, call forwarding, voicemail, call forwarding on busy etc.