Listener participation show at RKO -- dial free (4,5)
I believe the answer is:
talk radio
'listener participation' is the definition.
'at rko dial free' is the wordplay.
'free' indicates anagramming the letters.
'at'+'rko'+'dial'='atrkodial'
'atrkodial' is an anagram of 'TALK RADIO'.
'show' is the link.
(Other definitions for talk radio that I've seen before include "Broadcast chat" , "Programmes" , "Broadcast discussion" .)