Wear down staff in telecommunications company (5)
I believe the answer is:
erode
'wear down' is the definition.
(to erode is to wear down or decay)
'staff in telecommunications company' is the wordplay.
'staff' becomes 'rod' (both can mean a pole or stick).
'in' means one lot of letters goes inside another.
'telecommunications company' becomes 'ee' (I can't justify this - if you can you should believe this answer much more).
'rod' inserted inside 'ee' is 'ERODE'.
Can you help me to learn more?
(Other definitions for erode that I've seen before include "Wear away with weather" , "'Deteriorate, wear away (5)'" , "Grind down" , "go to pieces!" , "Corrode" .)