If you are on a Level3 circuit and not going through the interwebs, authentication is optional. If you are going to connect the peer straight to the 3300 they will have to add the entire subnet to their router config to allow audio to pass properly (they really don't like doing this and I do t blame them). That is a very basic overview. As Ralph said, there is much more. And I second the recommendation of MBG. Your life will be easier.