Telephone cartel (4)
I believe the answer is:
ring
This clue is a double definition.
'telephone' is the first definition.
(I know that telephone can be written as ring)
'cartel' is the second definition.
(both can mean a criminal group)
(Other definitions for ring that I've seen before include "Group of criminals maybe" , "Surround; reverberate" , "Circular, band of metal say" , "'It's a square, strangely, for boxers (4)'" , "Circle; telephone" .)