extensions.conf:

[voicemail]
exten => s,1,Ringing
exten => s,2,Wait(3)
exten => s,3,Answer
exten => s,4,Wait(0)
exten => s,5,Voicemail(u${RDNIS})
exten => s,6,Playback(vm-goodbye)
exten => s,7,Hangup
exten => s,106,MailboxExists(${CALLERIDNUM})
exten => s,107,Playback(bsky/blue-sky-communications)
exten => s,108,Playback(welcome)
exten => s,109,Voicemailmain
exten => s,110,Hangup
exten => s,207,Playback(bsky/blue-sky-communications)
exten => s,208,VoiceMailMain(${CALLERIDNUM})
;exten => s,208,VoiceMailMain(${CALLERIDNUM}|s)
exten => s,209,Hangup

zapata.conf:

signalling = pri_cpe
switchtype = dms100
group = 4
context = in-voicemail
channel => 25-47,49-71
---------
--- OR ---
---------

sip.conf:

[AS5350]
type=friend
username=               
secret=             
host=
context=in-voicemail             
dtmfmode=rfc2833                
canreinvite=yes
insecure=very
nat=no
disallow=all
allow=ulaw 
allow=g729
allow=g723