extensions.conf
==============================
[default]
exten => _1NXXNXXXXXX,1,Dial(SIP/allo/${EXTEN:1},20,r)

exten => 8000,1,Answer()
exten => 8000,2,Wait(2)
exten => 8000,3,Playback(tt-weasels)
exten => 8000,4,VoicemailMain()

.call file
==============================
Channel: Local/12145503519
MaxRetries: 0
RetryTime: 40
Context: default
Extension: 8000
Priority: 1