I noticed that in SMS hacking section there are great FM sound hacks of Ys and Phantasy Star but not for Wonder Boy III: The Dragon's Trap???
The guys at MEKA explained how this can be accomplished through Winhex:
;-----------------------------------------------------------------------------
; Wonder Boy III: The Dragon's Trap [SMS]
;-----------------------------------------------------------------------------
; Patch ROM to enable FM Unit support in European/US mode.
; The non-patched game uses the FM Unit only in Japanese mode.
; Author: Omar Cornut / Bock
;-----------------------------------------------------------------------------
[mekacrc: 9C7847B5CB3F875F]
ROM[025B] = 00, 00
;-------------
I have just patched it myself and it sounds so much better. I will gladly upload the prepatched ROM on the main site but i don't know how!