Hi Rui,
I'd like to make a test, when you have some time

Remember once, about a year ago, I gave you an extension number on my Asterisk PBX

That was when I had a public IP, which I no longer have, because now I sit behind a NAT private IP
BUT, "Hamachi" to the rescue

I installed Hamachi (Linux version) on my Asterisk box, so you can now connect to my Hamachi VPN IP, and connect with a VoIP client, such as Firefly. I haven't tried SIP, but IAX protocol works like a charm

So PM me for more info
Cheers,
-kwag