Secret codes for Android mobile operating system:

Phone and Battery information Code:      *#*#4636#*#*

Factory Data reset Code: *#*#7780#*#*

Full Factory Format Code: *2767*3855# (Dangerous)

GTalk Service Monitor Code: *#*#8255#*#*

Camera Firmware settings Code: *#*#34971539#*#*

Service mode Codes:

*#*#197328640#*#* 

 This code can be used to enter into Service mode. You can run various tests and change settings in the service mode.

WLAN, GPS and Bluetooth Test Codes:

WLAN test (Use "Menu" button to start various tests) :  *#*#232339#*#* OR *#*#526#*#* OR *#*#528#*#*

Shows WiFi MAC address :      *#*#232338#*#*

GPS test :   *#*#1472365#*#*

Another GPS test :  *#*#1575#*#*

 Bluetooth test :   *#*#232331#*#*

Shows Bluetooth device address :   *#*#232337#*#

Codes to launch various Factory Tests:

Packet Loopback :   *#*#0283#*#*

LCD test :  *#*#0*#*#*

Melody test :       *#*#0673#*#* OR *#*#0289#*#*

Device test (Vibration test and BackLight test) :       *#*#0842#*#*

Touch screen version :  *#*#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#*#*

Note: If you would like to try it, better you keep a backup copy of your data on the handset!