Asterisk basics -> Delayed Ring Group
;
[wait-op]
; Ask if the channel is available, if it is
; go to the next step. If it isn't go to no-op
; and skip the delay.
exten = _XX,1,ChanIsAvail(SIP/${EXTEN})
exten = _XX,n,GotoIf($[ "${AVAILCHAN}"="" ]?no-op|s-na|1:3)
; Increment the delay by a value of five.
exten = _XX,n,Set(DB(cross/delay-${key})=$[${DB(cross/delay-${key})}+5])
exten = _XX,n,Wait(${DB(cross/delay-${key})})
exten = _XX,n,Dial(SIP/${EXTEN})
 
[no-op]
; Do nothing
exten = s,1,NoOp(Dummy)
exten = s-na,1,NoOp(Channel is not available)
 
[hotline-0]
; Define a custom name for the caller ID. 
; This was an extra that I did
exten = s,1,Set(CALLERID(name)=hotline ${CALLERID(name)} ${CALLERID(num)})
; Set a key unique for each channel. So id doesn't matter how
; many calls we get, there will always exist just one key per channel
; This way we increase the delay only when we want to.
exten = s,n,Set(__key=${CHANNEL})
; Define the initial delay value on the database. That's even better than
; a global variable. One advantage, pointed out by a collegue of mine, is
; that when the process is over, you can delete the key from the DB.
exten = s,n,Set(DB(cross/delay-${key})=-5)
; Set all the devices as a single variable.
; Note that all of them use the "Local" context
exten = s,n,Set(dg0=Local/91@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/93@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/95@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/20@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/21@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/50@wait-op)
exten = s,n,Set(dg0=${dg0}&Local/22@wait-op)
exten = s,n,Dial(${dg0}|80)
; Manage the voicemail with a macro
exten = s,n,Macro(hotline-voicemail|${DIALSTATUS}|0)
; Delete the keys at hangup
exten = h,1,NoOp(DB_DELETE(cross/inc-${key})
exten = h,n,Hangup
 
[macro-hotline-voicemail]
; ${ARG1} Dialstatus
; ${ARG2} Whose voicemail?
exten = s,1,Set(CHANNEL(language)=de)
exten = s,n,Goto(s-${ARG1},1)
exten = s-BUSY,1,Voicemail(${ARG2},b)
exten = s-NOANSWER,1,Voicemail(${ARG2},u)
exten = s-CONGESTION,1,Voicemail(${ARG2},b)
exten = s-CHANUNAVAIL,1,Voicemail(${ARG2},u) 
   

Asterisk basics -> Voicemail
;
; *First thing is defining an ew context for the voicemail*
[voicemail]
exten = asterisk,1,NoOp(This extension takes us to check the voicemail)
exten = asterisk,n,NoOp(Caller ID : ${CALLERID(num)})
exten = asterisk,n,NoOp(Channel Type : ${CHANNEL(channeltype)})
exten = asterisk,n,GotoIf($[ "${CHANNEL(channeltype)}" = "SIP" ]?asterisk-sip,1)
exten = asterisk,n,GotoIf($[ "${CHANNEL(channeltype)}" = "IAX2" ]?asterisk-iax,1)
exten = asterisk-sip,1,NoOp(SIP Name : ${SIPCHANINFO(peername)})
exten = asterisk-sip,n,NoOp(Mailbox : ${SIPPEER(${SIPCHANINFO(peername)}|mailbox)})
exten = asterisk-sip,n,Macro(voicemail-general|${SIPPEER(${SIPCHANINFO(peername)}|mailbox)})
; *Now, there's no IAXCHANINFO on asterisk 1.2 - 1.4. But it will work if you have an IAX2 client*
; *that supports entering voicemail login info. (like voix phone)*
exten = asterisk-iax,1,NoOp(IAX automatic voicemail is not yet supported)
exten = asterisk-iax,n,Macro(voicemail-general)
 
 
; *Second thing is definig a Voicemail Macro.*
; *Think of this macro as of a function which performs a login for the voicemail.*
[macro-voicemail-general]
; ${ARG1} = User's mailbox
; *If the SIP 12 has the mailbox 30, then ${ARG1} = 30.*
; *But don't worry, this parameter is already given by the "asterisk" context previously defined.*
; Set the language for the voicemail message.
exten = s,1,Set(CHANNEL(language)=de)
exten = s,n,Answer()
exten = s,n,GotoIf($[ ${ISNULL(${ARG1})} ]?s-null,1)
; *In my case I had to put this wait in order for the greeting message to play completely.*
exten = s,n,Wait(1)
exten = s,n,VoiceMailMain(${ARG1})
exten = s,n,Hangup()
; *The extension s-null is called when ${ARG1} is empty*
; *In this case, we call VoiceMailMain withouth parameters and, if the client, say voix phone,*
; *has the voicemail login data configured, it will pass it automatically to asterisk.*
; *It may well be that you don't need the "Wait()" here*
exten = s-null,1,Wait(1)
exten = s-null,n,VoiceMailMain() 
exten = s-null,n,Hangup()
 
 
; *Finally, I included the "voicemail" context on the default context for my users.*
[default]
include = voicemail
...