From mezzoConsult C.B.:
Asterisk is a complete PBX in software. It provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in three protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware.
Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response, Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway).
Check the features section on the official Asterisk web site (http://www.asterisk.org) for a more complete list.
This version adds some custom modules by mezzoConsult (see http://mezzo.net/asterisk)
app_ldap - ldap support for dialplan.
app_notify - CallerID notification.
app_swift - support for Text-To-Speech Cepstral voices in the dialplan.
As previously announced, this release contains a large number of new features over the 1.2 series; see the CHANGES file in the distribution for the complete list. Before installing this release, be sure to read the UPGRADE.txt file as well, to be aware of changes that were made that will require you to change configuration files or dialplan entries.
This version contains numerous bug fixes. One of these is for a security issue in chan_sip. The issue is that SIP dialog history was being stored in memory regardless if the option for this was turned on or off. This could be abused to cause a system using chan_sip to run out of memory.