→Create a Ring Group: fail
<group name="Main" display-name="Main" extn="100" ddi="+441234567890" ring="101 102 103" type="all"/>
You will need to open the firewall if you are actually fire-walling traffic to the FireBrick - often people just firewall traffic to the LAN, and therefore all traffic to the FireBrick is allowed.
SIP and RTP traffic will need to be allowed
in to the FireBrick. This will need to be from the carrier, but also from external SIP phones if you have any.
Take a look at this wiki page for more info: [[FireBrick_2700#VoIP_Rules FireBrick_2700#VoIP Rules|FireBrick and VoIP Firewall]]