Bang bell cast in iron (6)
I believe the answer is:
fringe
'bang' is the definition.
(I've seen this before)
'bell cast in iron' is the wordplay.
'bell' becomes 'ring' (to give someone a bell is to ring them on a phone).
'cast in' is an insertion indicator.
'iron' becomes 'fe' (Fe is the chemical symbol for iron).
'ring' going within 'fe' is 'FRINGE'.
(Other definitions for fringe that I've seen before include "Less important" , "Ornamental border of threads" , "Border; hair on brow" , "Rim" , "Border; not mainstream" .)