This is virtually identical to the switchboard I trained on in 1969. I once became overwhelmed with calls and at serious risk of getting important callers mixed up, so I 'accidentally' pulled the plug out before quickly plugging the machine in again and apologising to those who called back for the 'technical fault'. I am still ashamed of my action that day. 
Anyone got any ideas for washing handkerchiefs

for most of my working time (not with the Post Office) until redundancy / ill health in 2000. 