"Diagram for conversion of existing telephones to fit new type boxes".

[an undated leaflet that came with a non-approved conversion
kit, and that I copied for future reference.  I pass on this 
information entirely without any endorsement or support, for 
educational value only.  It applies to the standard 700-series 
type phone that was in general use at the time that modular 
sockets were being introduced.  I have seen this in use, 
including the original bell actually working - contrary to some 
informants who said that it had to be changed for a high 
impedance bell - but I personally haven't used a phone like 
this, and BT won't find one at my house, I assure them  ;-)  ].

'INSERT MENTAL PICTURE OF RED TRIANGLE HERE'



(1)   (2)   (3)   (4)===(5)===(6) B (7)   (8)===(9)
                      A       /     ______/
                             |     |           C
(10)  (11)  (12)  (13)  (14) |(15) |(16)==(17)==(18)==(19)
              |              |     |        |
              |              |     |        |
            green          blue   red     white
           (spare)

"Instructions"

A. Remove strap between terminals 4 and 5 and insert 3.3kohm resistor.
B. Remove strap between terminals 6 and 7.
C. Place strap between terminals 17 and 18.
D. Connect line jack cord as shown:
green (spare) to 12, blue to 6, red to 8 and white to 17.

"New type sockets cannot be connected to shared service (party) lines".

(ajf says: party line phones would have been wired slightly 
differently anyway, so the above diagram would not help).