With a few friends of mine I found when speaking to them on there Galaxy S II’s, the speech sounds muffle and not very clear. This is because they do not hold the phone correctly and or close to there mouth which result in poor speech quality, however the remedy is to setup better volume levels as the phone factory default levels is set too low which result in poor speech quality.

By setting it to my recommended levels, not only does this resolve this issue, but also allows one to hold the phone whichever way you want without the result of poor speech quality. I have customized my Galaxy S II to the point where I got this issue sorted, with excellent speech quality. I have even done the same custom volume setting, on two friends of mines phones and since this setup the speech are clear and of good quality. The Samsung factory default settings on the Galaxy S II is set too low and incorrect which result in poor speech quality. Fine for when holding phone correctly in line and or close to your mouth, however out of line would result in poor speech quality.

I have played around with the level and found the setting of ” 90 to 92″ to be correct and working well.

Please look at the pic,
tap on 4 and set to 88
tap on 5 and set to 92.
Some would ask what is the settings from 1 to 5, (look at the pic) this is the increments volume adjustments when you use your volume buttons from soft to loud.

Please note; you could use the same settings for headset and speaker phone. Please note; setting for speaker higher then 92 will result in your sound distorting.

CAUTION : this is not for the novice. If you do not know what you doing, could result in damaging your phone.

Tips and Tricks: Boost the Samsung Galaxy S II’s incall volume
If you find the Samsung Galaxy S II’s incall to be a bit too low for your preference even at the maximum level, here is a tip for you. By default, the maximum value goes only up to 88 and not 90~92, but there is an easy way to rectify that.

1) Dial and call *#*#197328640#*#*
which will open the service mode menu
2) Select [5] AUDIO
3) Select [1] (VOICE CALL)
4) Select HANDSET
5) Select Volume
6) Select SRC Speech RX Volume
7) Select [5] 5_lvl : 87
8) Tap the Menu utton
9) Select Key Input

Source: http://www.mobile88.com/news/read.asp?file=/2011/7/8/20110708144225&phon…