If you took the advice in the article, A possible way to thwart SIP hack attempts on your Asterisk (or other) PBX server, please be aware that an important note has been added:

IMPORTANT: Be sure to have a separate iptables rule (higher on the list than those above) that allows connections to port 5060 from devices on your local network. Otherwise, you may find that new extensions that you are adding for the first time will not register with your Asterisk server, or that after a system reboot, none of your local extensions will register!

Please take heed of that note, or you may be one power failure or reboot away from discovering that none of your local extensions are able to register with your PBX server.