VoIP – Voice Over IP (Internet Protocol) – Telephones over the Internet. The software of choice for running a PC based PBX is Asterisk. If working in the command line and getting your fingers dirty you can always try AsteriskNOW which is an open source Software Appliance on a bootable CD (downloadable ISO image). The foremost source of information about everything VoIP is without a doubt the www.voip-info.org wiki.
Asterisk is not the easiest way to use VoIP for the average end user. This is designed as a server for servers. An excellent understanding of Linux is pretty much essential. You will need to know how to how to compile source code and edit complex configuration tools. However saying that once you get your head around how the Asterisk configuration files are structured it’s not that hard. If any of that scares you then I suggest you use AsteriskNOW, it’s really a PBX in a can.
Why use Asterisk? Well, Asterisk is for people and companies that want to either replace their landline phone lines with either a Soft Phone or a VoIP Phone (somtimes called a Hard Phone). A Soft Phone is a bit of software that runs on your computer and with the use of a headset with a microphone you can make and receive calls using VoIP services. The VoIP (IP Phone / Hard Phone) is a device that looks the same as a normal phone but differs in that it plugs into a network connection or uses Wi-Fi (Wireless Network). These are standalone phones in so much as they don’t require the use of a PC for anything other then the initial configuration, however most support some form of automatic configuration during the boot-up phase of the phone.