all credit goes to TheOne of SymbianTalk~ FYI These codes have been obtained by decoding various .apk files present in the phone firmware.
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*#*#4636#*#*
This code can be used to get some interesting information about your phone and battery. It shows following 4 menus on screen:

Phone information
Battery information
Battery history
Usage statistics
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*#*#7780#*#*
This code can be used for a factory data reset. It'll remove following things:

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

Current system software and bundled applications
SD card files e.g. photos, music files, etc.
PS: Once you give this code, you get a prompt screen asking you to click on "Reset phone" button. So you get a chance to cancel your operation.
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*2767*3855#
Think before you give this code. This code is used for factory format. It'll remove all files and settings including the internal memory storage. It'll also reinstall the phone firmware.
PS: Once you give this code, there is no way to cancel the operation unless you remove the battery from the phone. So think twice before giving this code.
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*#*#34971539#*#*
This code is used to get information about phone 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 will stop working and you'll need to take your phone to service center to reinstall camera firmware.
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*#*#7594#*#*
This one is my favorite one. This code can be used to change the "End Call / Power" button action in your phone. Be 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.
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*#*#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.
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*#*#197328640#*#*
This code can be used to enter into Service mode. You can run various tests and change settings in the service mode.
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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
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*#*#8255#*#*
This code can be used to launch GTalk Service Monitor.
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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
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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
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NOTE: All above codes have been checked on Google Android phone Samsung Galaxy I7500 only but they should also work in other Google Android phones.

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Added on November 5, 2010, 1:32 pmplease feedback on codes that work on your Android~

This post has been edited by sexualpower: Nov 5 2010, 01:47 PM

not bad, not bad..trying now! but not all code working on my wildfire

This post has been edited by RisK.yO: Nov 5 2010, 02:34 PM

Nice info.. Thx for sharing.. :-D

only this code *#*#4636#*#* can work on my se x10 mini pro...

Regarding above code, what happen to contact no? Is it will be remove too?

when i enabled this option on my galaxy 5, i couldn't connect to my network provider

List of codes working on phones;
1) Wildfire; *#*#4636#*#* only
2) SE X10 Mini pro; *#*#4636#*#* only

arafat, do report back to us so if your problem persists, tq~