Overview of Asterisk Versions:
https://wiki.asterisk.org/wiki/display/AST/Asterisk+Versions
Download Asterisk:
http://downloads.asterisk.org/pub/telephony/asterisk/
Download Asterisk Admin Guide:
https://wiki.asterisk.org/wiki/display/AST/Asterisk+Exported+Documentation
Asterisk Module Stats (Find out what features are deprecated? Better start using the core applications for future support):
https://wiki.asterisk.org/wiki/display/AST/Asterisk+Module+Support+States
Configuration and Operation:
https://wiki.asterisk.org/wiki/display/AST/Configuration+and+Operation
Great place to for VoIP knowledge base:
http://www.voip-info.org/
Information regarding Upgrade changes:
Please check the UPGRADE*.txt documentation in the Asterisk source you downloaded.
Extras:
Call Center Monitoring:
http://queuemetrics.com/
Operator Solution:
http://www.voiceoperatorpanel.com/
VoiceXML/CCXML Gateway:
http://www.voxeo.com/
http://www.vxml.org/frame.jsp?page=w3cprops.htm
