This will probably be most useful to GD owners not in AU - who buy a 'GD-01' (AU market) headunit. However it may still be useful for those looking to mod.
A number of eBay images show (none crystal clear) the pinout of the 'GD-01' audio headunit (seemingly only AU market) - but I hadn't seen the pinout online...
So I made one referenced to a 'generic' GD i30/'Elantra GT' headunit pinout - generic used to describe the look of 'bog-standard' (small screen, no touch, two rows of buttons) headunit fitted in a number of markets (NZ, UK, NAM?, etc.). The 'generic' pinout may have some market specific functions labelled (e.g. TMU) - but it appears Hyundai doesn't move functions between pins... if not present it appears the pin isn't used.
And here is an image of the pinout label from a GD-01:
