[general]
register =>0812341234:MySIPPass@sip.internode.on.net/s
registertimeout=20
context=incoming
allowoverlap=no
bindport=5060
bindaddr=192.168.0.3
srvlookup=no
subscribecontext=from-sip

; The SIP provider
[VoIPProvider]
canreinvite=no
username=0812341234
fromuser=0812341234
secret=MySIPPass
context=incoming
type=friend
fromdomain=sip.internode.on.net
host=sipconnect.internode.on.net
dtmfmode=rfc2833
disallow=all
allow=alaw
allow=ulaw
nat=yes
insecure=very

; ext 100
[100]
type=friend
host=dynamic
secret=MyPass123
context=internal
mailbox=100@default
callgroup=1
pickupgroup=1
dtmfmode=rfc2833
canreinvite=no

; ext 200
[200]
type=friend
host=dynamic
secret=MyPass123
context=internal
callgroup=1
pickupgroup=1
dtmfmode=rfc2833
canreinvite=no
Here is the “/etc/asterisk/extension.conf” file:

[incoming]
; Ring on extension 100, 200 and the mobile phone.
exten => s,1,Answer()
exten => s,n,Dial(SIP/100&SIP/200&SIP/VoIPProvider/*320423456789,150,r,t,)

; Pass unanswered call to a mobile phone
exten => s,n,Dial(SIP/VoIPProvider/*320423456789,150,r)

; Still not answered? Pass unanswered calls to voicemail
exten => s,n,Voicemail(100,u)
exten => s,n,Hangup

[outgoing]
; Outbound calls can be routed based on the number of digits dialled (or the value of the first few digits)
exten => _XXXXXXXXXXXXXXX,1,Dial(SIP/VoIPProvider/${EXTEN})
exten => _XXXXXXXXXX,1,Dial(SIP/VoIPProvider/${EXTEN})
exten => _XXXXXX,1,Dial(SIP/VoIPProvider/${EXTEN})

[internal]
; Calls between employees (between extensions)
exten => _XXX,1,Dial(SIP/${EXTEN})

; Calls to ext 100
exten => 100,1,Dial(SIP/100,20)
exten => 100,n,VoiceMail(100,u)
exten => 100,n,Hangup

; Calls to ext 200
exten => 200,1,Dial(SIP/100,20)
exten => 200,n,Hangup
- See more at: http://agix.com.au/blog/?p=2656#sthash.lv1ZrEvf.dpuf