Asterisk is complete PBX software which runs on Linux, Windows, BSD and OSX which works in four different protocols for VoIP interconnecting with almost all equipment regarding to the telephony. It is very affordable software among the available softwares in market.

It provides so many features like other VoIP services. The major services are voicemail service with directory, call conferencing, Interactive voice response, caller ID and call queuing. It even includes voice conferencing which allows you to talk with more than two people at the same time. Asterisk do not needs any additional hardware. But it needs a simple software driver to implement your old hardware as a non-portable timing mechanism. You can use more than one VoIP service providers for incoming and outgoing calls because than can be handled by different VoIP providers. Asterisk supports number of equipment like Asterisk sponsored hardware Digium for use of digital and analog telephony equipment. Asterisks FXO and FXS cards are more popular for small installations.

Asterisks can be found in two edition or versions. First one is Asterisk Open Source Edition and another is called Business Edition. Open source version has services like unlimited-side conference, bridge switched or packet data and voice mail. Imagine how good is to talk 10 people at once in telephone. Asterisk-centric pound key Linux, SIP and IAX support, VoIP capability are more features of Open Source Edition. This version also features converged telephony, full PBX capability, TDM capability. Business Edition adds some other facilities on open source edition. Some of them are Asterisk Technical Manual, Quick-start Guide, and Commercial License with Legal Protection, 240 Simultaneous Calls, Tech Support for Install and Bug Resolution, Free Upgrades and Tech Support for One Year, Access to Business Edition Portal for One Year, Special Offers for Partner Products.

Asterisk obviously needs high speed internet to communicate people. It connects pc client to each other through and Asterisk server which uses a Linux/Unix OS. Asterisk uses different channel protocols to pass the calls. H323, SIP, IAX are popular forms. The softwares can be varying depending upon the type of those channel protocols. Let's say, if are a registered on an Asterisk PBX (or other PBX) as a SIP user, you should use a SIP phone client such as X-Lite. Similarly iaxcomm is for IAX user. SIP and IAX client configuration lets you to register as SIP and IAXuser which includes the adjustment of all asterisk and client phone settings.

All the information about user, calls, voicemails and everything are written in extension.conf. Like all information about the users are stored in sip.conf and voicemails in voicemail.conf. Those files are located in /etc/asterisk. User should be connected to PBX for call handling and users using PCs with softphones for calling internally and externally. User will have username and password just like other VoIP systems. Only that will allow you to call someone who is registered. Hence, you must be a registered user to receive or make a call. Non-Asterisk users can't access any of asterisk services.

User must reload the entire conf file again every time you they make a change in any of conf files. Otherwise they won't work. That can be done by tying 'reload' in Asterisk Command Line Interface (CLI). Open Source Edition is enough for your corporate business but Business Edition can be better. You must need to have a Linux OS computer and Asterisk has to be installed.