Have you tired using
http://www.whatsmyip.org/ to get your external IP and then get someone else to see if they can connect from outside with the IP and the port
for example they would use
http://95.135.17.22:4040 if your IP was 95.135.17.22
Depending on how things are set up on your router that should test your incoming connection.
If they see the username and password page then it worked.
If not then you have to sort out your routers port forwarding. I suggest doing it manually but some prefer the UPnP method. You need to map the external port 4040 to the internal IP address of your PC and also at port 4040.
If your having trouble with the subsonic.org DNS setup you could try using a DynDNS account. They are free but you have to remember to put the ":4040" at the end of the URL and you have to find a way to update the IP address if your using a dynamic IP.
The subsonic.org method will work in most situations though.
Of course if your SIP has given you a static IP then you can just use the IP and port number like above and forget about all the DNS or subsonic naming.
Hope that helps some.
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