Note that the commands used in "exten =>" lines in extensions.conf are called applications. A list of these can be obtained from the Asterisk console with the command
show applications
To get help on a particular command, try
show application command
Another good source of information about Asterisk is Voip-Info.Org. For example, detailed documentation on commands can be found
here, while information about extensions.conf can be found
here.
Source: http://lists.digium.com/pipermail/asterisk-users/2003-March/008369.html
SIP callgroup feature similar to ZAP groups : Could not find information whether this is possible.
See also: http://lists.digium.com/pipermail/asterisk-users/2005-May/105388.html
One page links to AsteriskNotes:
lib/main.php:944: Notice: PageInfo: Cannot find action page