Mine

sip.conf (snippet)

[general]
port = 5060
bindaddr = 0.0.0.0
context = default
disallow = all
allow = g729
allow = gsm
allow = ulaw
allow = alaw

[Accela]
disallow=all
allow=g729
allow=ulaw
allow=alaw
type=friend
host=64.124.221.10
dtmfmode=rfc2833
canreinvite=no
insecure=very

[1031]
disallow=all
allow=g729
allow=gsm
allow=ulaw
allow=alaw
type=friend
username=1031
secret=1031
host=dynamic
permit=0.0.0.0/0.0.0.0
dtmfmode=rfc2833
qualify=yes
mailbox=1031
nat=yes
canreinvite=no
insecure=very

extensions.conf

SIPACCOUNT1=SIP/Accela

;### Accela Trunk
exten => _01NXXNXXXXXX,1,Set(CALLERID(number)=8663750773)
exten => _01NXXNXXXXXX,n,Set(MONITOR_EXEC=/root/move_files.sh)
exten => _01NXXNXXXXXX,n,Set(DIREC=/var/spool/asterisk/monitor) 
exten => _01NXXNXXXXXX,n,Set(CALLFILENAME=${TIMESTAMP}_${EXTEN:1}_OUTBOUND_${CALLERIDNAME}) 
exten => _01NXXNXXXXXX,n,MixMonitor(${CALLFILENAME}.gsm|bW(4)|/root/move_files.sh ${CALLFILENAME}.gsm)
exten => _01NXXNXXXXXX,n,Dial(${SIPACCOUNT1}/${EXTEN:1},30,to)
exten => _01NXXNXXXXXX,n,congestion()
exten => _01NXXNXXXXXX,n,Hangup()