Middle name put first in place for telephone operators (4,6)
I believe the answer is:
Here is my best explanation:
'place for telephone operators' is the definition.
'middle name put first' is the subsidiary indication.
'middle' becomes 'centre' ('centre' can be a synonym of 'middle').
'name' becomes 'call' (a name is a call-sign**).
'put first' says to put letters next to each other.
'centre' put after 'call' is 'callcentre'.
'in' is the link.
(Other definitions for call centre that I've seen before include "Office with many phones", "Telephone answering office", "Phone here for help" and "Workplace".)