A lot of ISP's and BT themselves refer to what they call the "test socket". The standard master box in most modern homes is an NTE5, we sell the latest version, the NTE5A (:http://www.run-it-direct.co.uk/BTsocketNTE5.html), which has a filter on the bell wire circuit for improved ADSL performance. The NTE5 is designed so that if you undo the front faceplate and take it off there is still a BT 631A socket behind. This is what is being refered to when they describe the "test socket". All they are really doing is disconecting any extension wiring you may have and presenting a BT socket that is wired directly to BT's network, if you can't get good ADSL performance(or a voice line without any interference) when plugging into this socket then the problem lies firmly with BT's network/wiring. This removable faceplate can also be exchanged for an ADSL filtered version for a neater installation http://www.run-it-direct.co.uk/BTNTE5ADSLfaceplate6way.html