Samsung Secret Code

Code
phone information : *#*#4636#*#*
hard reset* : *2767*3855#
factory reset** : *#*#7780#*#*
change end call/power option : *#*#7594#*#*
service mode : *#*#197328640#*#*
file copy screen (backup media files) : *#*#273283*255*663282*#*#*
wlan test : *#*#526#*#*
shows wifi mac address : *#*#232338#*#*
gps test : *#*#1472365#*#*
another gps test : *#*#1575#*#*
bluetooth test : *#*#232331#*#*
shows bluetooth device address : *#*#232337#*#
gtalk service monitor : *#*#8255#*#*

codes to launch various factory tests:
packet loopback : *#*#0283#*#*
lcd test : *#*#0*#*#*
melody test : *#*#0673#*#*
device test (vibration test and backlight test) : *#*#0842#*#*
touch screen version -warning!!- : *#*#2663#*#*
touch screen test : *#*#2664#*#*
proximity sensor test : *#*#0588#*#*
ram version : *#*#3264#*#*

codes to get firmware version information:
pda, phone, h/w, rfcalldate : *#*#4986*2650468#*#*
pda and phone : *#*#1234#*#*
fta sw version : *#*#1111#*#*
fta hw version : *#*#2222#*#*
pda, phone, csc, build time, changelist number : *#*#44336#*#*

Nb:
hard reset will erase all file and setting in memory, it`s like reformat the firmware. Once you press it, there is no turning back.
factory reset only delete the account, system and setting application.
And be careful with *#*#2663#*#* (touch screen version), don`t upgrade the version it`s same like do a hard reset