"Your turn," on a walkie-talkie (4)
I believe the answer is:
'your turn on a walkie-talkie' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for over that I've seen before include "settled" , "In the sky?" , "Directly above" , "Having gone < to America" , "Finished, done" .)