Air Force One for example key in visits (4,4)
I believe the answer is:
call sign
'air force one for example' is the definition.
(call sign for a plane carrying the US president)
'key in visits' is the wordplay.
'key' becomes 'g' (musical key).
'in' is an insertion indicator.
'visits' becomes 'calls in' ('call in' can be a synonym of 'visit').
'g' placed inside 'callsin' is 'CALL SIGN'.
(Other definitions for call sign that I've seen before include "Unique designation in radio communications" , "A wireless operator's identification" , "Radio ID" , "Identifying code of sender or receiver of broadcast message" , "Radio identification" .)