From sip.conf
=============

[201]
type=friend
context=default
secret=201
host=dynamic
dtmfmode=rfc2833
username=201
allow=ulaw
progressinband=no
mailbox=200@default

From extensions.conf (the part that handles the outside connections)
====================================================================

[numberplan-custom-1]
plancomment = DialPlan1
include = default
exten = _9.,1,Macro(trunkdial,${trunk_1}/${EXTEN:1})
comment = _9.,1,Outgoing,custom
exten = _999,1,Macro(trunkdial,${trunk_1}/${EXTEN:0})
comment = _999,1,UK Emergency Services,standard
exten = _112,1,Macro(trunkdial,${trunk_1}/${EXTEN:0})
comment = _112,1,EURO Emergency Services,standard