Ring Ring, endless single for composer (7)
I believe the answer is:
bellini
'for composer' is the definition.
(I've seen this before)
'ring ring endless single' is the wordplay.
'ring' becomes 'bell' (both can mean to call on the phone).
'endless' means to look at the middle letters.
'single' becomes 'I' (one).
The middle of 'ring' is 'in'.
'bell'+'in'+'i'='BELLINI'
(Other definitions for bellini that I've seen before include "Musical artist" , "member of painting family" , "Italian opera composer (Norma)" , "Cocktail; composer of opera Norma" , "scorer" .)