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 stick or cane).
'in' means one lot of letters goes inside another.
'telecommunications company' becomes 'ee' (I can't explain this - if you can you should give a lot more credence to this answer).
'rod' inserted within '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" .)