Asterisk PBX Introduction
What Is PBX ?
      PBX actually is PABX or Private Automatic Branch Exchange. It is private because the enterprise owns it, not the telephony  company.  Nowadays, PBX equipment is digital. PBX is less expensive to use than separate phone line in an enterprise. PBX  provide a place for trunk or multiple phone. A PBX provides features and capabilities not available with direct connections to the public switched telephone network (PSTN). There's a lot of PBX features like interactive voice response (IVR), access control,  music on hold, call waiting, caller id, call transfer and many more.
What is VOIP ?
    

VOIP or IP Telephony and also called Internet telephony, is the technology that makes it possible to have a telephone  conversation where the signal is carried over the Internet or a dedicated network in Internet Protocol (IP) packets, instead of  over dedicated voice transmission lines. This allows the elimination of circuit switching and the associated waste of bandwidth.  Instead, packet switching is used, where IP packets with voice data are sent over the network only when data needs to be sent,  i.e. when a caller is talking. One of the advantage of using VOIP is lower cost per call especially for long distance calls.

 
Introduction To Asterisk
Compatible Phone
 Some of the phone that can be used together with Asterisk  

  1. XTEN SIP phone ( http://www.xten.com )
  2. ESTARA SIP phone ( http://www.estara.com )
  3. GnoPhone Linux SIP phone ( http://www.gnophone.com )
  4. Asterisk IAX phone ( http://www.sokol-associates.com )
  5. Asterisk IAC Phone ( http://iaxclient.sourceforge.net/iaxcom )
  6. Cisco 7960 ( http://www.cisco.com )

Asterisk Management System
 1. Astegui with Vicidial - http://astguiclient.sourceforge.net
 2. AMP ( Asterisk Management Portal ) - http://coalescentsystems.ca/index.php
 3. Areski Prepaid System - http://areski.net/areskicc-doc-v2
 4. Asterisk @ Home - http://asteriskathome.sourceforge.net
 5. A2Billing - http://www.areski.net/a2billing
Other Related Applicatoin / Software
 1. FOP ( Flash Operator Panel ) - A simple and easy application for Asterisk operator. With FOP, we can see incoming call  and transfer call to the other extension. Go to http://www.asternic.org for more information
VOIP Company
Book About PBX, VOIP Or Asterisk
 1. VOIP Telephony With Asterisk ( Paul Mahler, Signate LLC 2005 )
References
 1. VOIP Telephony With Asterisk ( Paul Mahler, Signate LLC 2005 )
 2. http://www.voip-info.org
Links

Google
Search For IP PBX, VOIP, Asterisk in Google