azphotog: I don't own either of the 5xx series Obi machines but I am assuming they have a built-in web page similar to the other devices? The Obi 200 [or 202] does not support Obiline "Out of the box" however when you go into the web page settings, the sections pertaining to LINE are still there. I would think the 5xx would probably be the same. If that is the case all you should have to do is plug the adapter in and Enable the line port. Of course you will probably have to mess with the digit map(s) and set the outbound and inbound routing up the way you want them to work. I have an adapter ordered but it will be quite a while before I get to experiment. Hope this helps.