Might this be of some help?
Left in Jumper(s). A process in which a Public Switched Telephone Network (PSTN) line pair is only switched off in software, and remembered, so that software can switch on again when required. The jumper wire pair at the Main Distribution Frame (MDF) is left in place, instead of having to be removed.
A bit more poking around shows this is related to LLU provision.
Of the phone numbers I have checked, those on a non-BT telephone service have left in jumpers and those on BT have not.
Edited by caffn8me (Sun 17-May-15 08:48:43)