*#*#4636#*#*

This shows the following information about your phone and battery:

Phone information
Battery information
Battery history
Usage statistics

*#*#7780#*#*

This performs a factory data reset, and will remove the following:

Google account settings stored in your phone
System and application data and settings
Downloaded applications
It will NOT remove:

Current system software and bundled applications
SD card files e.g. photos, music files, etc.
PS: This one asks for a confirmation, so if you do get a chance to change your mind.

*2767*3855#

Don’t try this one unless you’re sure. This code is used for factory format, and will remove all files and settings including the internal memory storage. It will also reinstall the firmware.

PS: Once you give this code, there is no way to cancel the operation unless you remove the battery from the phone, and even then, you run the risk of bricking your phone.

*#*#34971539#*#*

This code is used to get information about the camera. It shows following 4 menus:

Update camera firmware in image (Don’t try this option)
Update camera firmware in SD card
Get camera firmware version
Get firmware update count
WARNING: Never use the first option otherwise your phone camera may stop working, and there is really no reason to update the camera firmware anyway.

*#*#7594#*#*

This code will change the “End Call / Power” button action on your phone. By default, if you long press the button, it shows a screen asking you to select any option from Silent mode, Airplane mode and Power off.

You can change this action using this code. You can enable direct power off on this button so you don’t need to waste your time in selecting the option.

*#*#273283*255*663282*#*#*

This code opens a File copy screen where you can backup your media files e.g. Images, Sound, Video and Voice memo.

*#*#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:

*#*#232339#*#* OR *#*#526#*#* OR *#*#528#*#* – WLAN test (Use “Menu” button to start various tests)

*#*#232338#*#* – Shows WiFi MAC address

*#*#1472365#*#* – GPS test

*#*#1575#*#* – Another GPS test

*#*#232331#*#* – Bluetooth test

*#*#232337#*# – Shows Bluetooth device address

*#*#8255#*#*

This code can be used to launch GTalk Service Monitor.

Codes to get Firmware version information:

*#*#4986*2650468#*#* – PDA, Phone, H/W, RFCallDate

*#*#1234#*#* – PDA and Phone

*#*#1111#*#* – FTA SW Version

*#*#2222#*#* – FTA HW Version

*#*#44336#*#* - PDA, Phone, CSC, Build Time, Changelist number

Codes to launch various Factory Tests:

*#*#0283#*#* – Packet Loopback

*#*#0*#*#* – LCD test

*#*#0673#*#* OR *#*#0289#*#* – Melody test

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

*#*#2663#*#* – Touch screen version

*#*#2664#*#* – Touch screen test

*#*#0588#*#* – Proximity sensor test

*#*#3264#*#* – RAM version