Greek character involved in radio talks (4)
I believe the answer is:
iota
'greek character' is the definition.
(letter from the Greek alphabet)
'involved in radio talks' is the wordplay.
'involved in' says the answer is hidden in the clue.
'IOTA' is hidden in the letters of 'radio talks'.
(Other definitions for iota that I've seen before include "Smidgeon" , "Gr. letter; small amount" , "Foreign character" , "Jot, particle" , "Just a jot, from Greek alphabet" .)