Originally Posted by mastermind1024

Don't use any app..
Go into engineer's mod by *#*#8888#*#* (see 1st post)
Tap "Proximity Sensor Adjust"
Keep your hand abt 3 cm.(n not just 1 cm as phone says) from upper part of phone(over speaker area)
Let it calibrate n it will say done.
Now try calling,it will work perfectly.