@ianobi - yes it is a little messy, it was just what I could find to provide the right conversion from BT to modem connector (rj11). The ADSL filter is used because it's output (line side) is a modem connection (rj11) and of course it has a standard BT socket for the input from the phone, so that meant I could use a standard modem cable that I had.
I'll see if I can test which pins are connected to where on my current mess of wires and otherwise try looking to see what else I have around the house.
@dircom - I've not setup a Ip phone service yet, no, but I don;t see that as relevant, I'm just trying to do the first step of connecting a phone to the Obi110 so I can register it etc. But currently the phone doesn't seem to be talking to the OBi, presumably as ianobi is suggesting, because the wrong pins are connected. The phones can all make calls normally when plugged into the wall socket normally. Yes, ADSL. And yes, I am connecting the phone to the phone jack on the OBi.