A) Enter service mode by typing below code on your dialer :
*#*#197328640#*#*
click the following:
[5] AUDIO
[1] NB (VOICE CALL)
Choose Handset, headset, Speaker (which ever you want higher volume)
[1] VOLUME
[1] SRC Speech RX Volume
Change default values and higher the values any number of your choosing, here is an example:
[0]0_lvl : 68
[1]1_lvl : 72
[2]2_lvl : 76
[3]3_lvl : 80
[4]4_lvl : 84
[5]5_lvl : 88 Higher these values to until hear volume improvement.
