Try this, finf it else where, http://forum.vodafone.co.uk/t5/Samsu...ow/td-p/761245
I’ve investigated this issue, and it does seem to be a general one, found across all networks. The general fix is to access the service mode, and alter the default max volume for a headset call as follows:
•Enter this number *#*#197328640#*#*
•This will open the service mode menu.
•Select option  AUDIO
•Select option  (VOICE CALL)
•Select option  HEADSET
•Select option  Volume
•Select option  SRC Speech RX Volume
•Select option  5_lvl : 87
•Press the menu button (left side)
•Choose Key Input
•Enter a value between 0 and 100, with 100 the loudest setting.
•Then press the menu button and select back this will save (don't use the right side back key you normally use to navigate the phone or you will quit out of the settings).
•Keep selecting the menu and back until you exit the service mode menu.
You will also note you can change volume settings for other things like Bluetooth, handsets, video call etc.