Reg key HKLM\System\State\Touchlock . Set to 0 -> screen enabled, set to 1 -> screen locked
is the key responsable for locking the touchpad once a call is made, problem with this is if you are navigating a voicemail or automated menu this can be annoying.
The text below is a mortscript workaround which will disable this as a workaround, simply copy the lines between code paste into a text file & save as a *.mscr file e.g. no_screen_lock.mscr copy to the phone & run it,it will check & change the reg key to "0" everytime the phone sets it to "1" enabled.if you soft-reset the phone you will need to run the script again, if i figure out or find a way to permantly disable this option I will update.
CODE
# No_screenlock.mscr
# Script to prevent i900 from locking display while using Phone - (c) 2008 Juicey
#
# Set this to desired delay value in millisecs
delay=500
While ( 1 )
If wndActive "Phone"
regReadDword HKLM,"System\State","Touchlock",tlock
If equals %tlock%,1
regWriteDword HKLM,"System\State","Touchlock",0
EndIf
EndIf
Sleep %delay%
EndWhile
