context=default			; Default context for incoming calls
bindport=5060			; UDP Port to bind to (SIP standard port is 5060)
bindaddr=0.0.0.0		; IP address to bind to (0.0.0.0 binds to all)
srvlookup=yes			; Enable DNS SRV lookups on outbound calls
allow=ulaw			; Allow codecs in order of preference
relaxdtmf=yes			; Relax dtmf handling
useragent=BillsPBX		; Allows you to change the user agent string

nat=yes                                 : Duh <-
canreinvite=no                          : Can't allow phones from the inside to try and re-invite, the ports are already force forwarded.
externip=1.2.3.4                        ; Change this to YOUR WAN IP.
localnet=192.168.0.0/255.255.0.0        ; Change this if needed (already accounts for anything starting with 192.168)