If you have ever setup an asterisk box then you know some changes are in the configuration. One of those challenges is being behind a nat or router. The issue usually arises when you use the ivr and you dont receive DTMF tones to your ivr. I use ViaTalk for service and their support staff clued me into the problem. I had to externhost=my.dyndns.com in your sip_nat.conf does not solve this problem, or at least didnt for me so I had to write my own dynamic dns update script using php only because it was quick but you can do this is bash probably just as easily.
