Unconventional iron telephone kept inside (6)
I believe the answer is:
fringe
'unconventional' is the definition.
(fringe can mean unconventional or specialist)
'iron telephone kept inside' is the wordplay.
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'telephone' becomes 'ring' (synonyms).
'kept inside' means one lot of letters goes inside another.
'fe' placed around 'ring' is 'FRINGE'.
(Other definitions for fringe that I've seen before include "bang of Detroit" , "Less important" , "(Tasselled) border" , "Hair across the forehead" , "Tasselled edging" .)