"P2P Telephony Explained — For Geeks Only" http://skype.com/products/explained.html No, you do not need any firewall changes. But you can. I might get an account for Skype-out. Are there any good alternatives without a monthly fee? I don't need an incoming number, since Telstra force us to keep the land-line with ADSL. Although it might be handy to have a US number.