Samsung loopback, cencor & many more test.

Loopback test *#0283#
*#0673# (Audio Test Mode)
*#0*# (General Test Mode)
*#872564# (USB Logging Control) 
*#4238378# (GCF Configuration)
*#197328640# – Service mode for testing

Android Common Codes

Description	Code
Testing Menu	*#*#4636#*#*
Display Info about device	*#*#4636#*#*
Factory Restore	*#*#7780#*#*
Camera Information	*#*#34971539#*#*
Completely Wipe device, install stock firmware	*2767*3855#
Backup all media files	*#*#273283*255*663282*#*#*
Wireless LAN Test	*#*#232339#*#* OR *#*#526#*#*
Change Power button behavior	*#*#7594#*#*
Quick GPS Test	*#*#1472365#*#*
Test mode for service activity	*#*#197328640#*#*
Wi-Fi Mac Address	*#*#232338#*#*
Another GPS test	*#*#1575#*#*
Packet Loopback Test	*#*#0283#*#*
Audio Test	*#*#0673#*#* OR *#*#0289#*#*
Vibration and Backlight test	*#*#0842#*#*
Check touch screen version	*#*#2663#*#*
LCD test	*#*#0*#*#*
Touch Screen test	*#*#2664#*#*
Proximity sensor test	*#*#0588#*#*
RAM version	*#*#3264#*#*
Bluetooth test	*#*#232331#*#*
Field Test	*#*#7262626#*#*
Check Bluetooth device address	*#*#232337#*#
Google Talk service monitoring	*#*#8255#*#*
PDA, Hardware, Phone and RF Call Date info	*#*#4986*2650468#*#*
PDA and Phone firmware check	*#*#1234#*#*
FTA hardware version	*#*#2222#*#*
FTA software version	*#*#1111#*#*
Displays IMEI number	*#06#
Enables voice dialing logging mode	*#*#8351#*#*
Disables voice dialing logging mode	*#*#8350#*#*
Brings up Epst menu	##778 +call
Displays Build time and change list number	*#*#44336#*#*
Remove Google account setting	*#*#7780#*#*
Reinstall the firmware	*2767*3855#
Used to enter into Service mode	*#*#197328640#*#*
Battery Status	*#0228#
Data create menu	*#273283*255*3282*#
Data usage status	*#3282*727336*#
OTA update menu	*#8736364#
RF band selection	*#2263#
Diagnostic configuration	*#9090#
USB 12C mode control	*#7284#
USB logging control	*#872564#
Debug dump menu	*#746#
System dump mode	*#9900#
Shows Build time change list number	*#*#44336#*#*
NAND flash serial number	*#03#
Real time clock test	*#0782#
Light sensor test	*#0589#
Quick test menu	*#7353#
Execute from Emergency dial screen to unlock PUK code	**05***#

Samsung Secret Codes

Display IMEI number	*#06#
Display current firmware	*#1234#
Diagnostic and general settings mode	#*#4636#*#*
Factory soft reset	*#*#7780#*#*
To display product code	*2767*4387264636#
GPS test settings	*#*#1472365#*#*
Service mode main menu	*#*#197328640#*#*
SW & HW Info	*#12580*369#
Bluetooth Address	*#232337#
ADC Reading	*#0228#
RF Band Selection	*#2263#
Ciphering Info	*#32489#
Bluetooth Test Mode	*#232331#
Diagnostic Configuration	*#9090#
WLAN Test Mode	*#232339#
Vibration motor test	*#0842#
WLAN MAC Address	*#232338#
USB I2C Mode Control	*#7284#
Audio Test Mode	*#0673#
General Test Mode	*#0*#
USB Logging Control	*#872564#
GCF Configuration	*#4238378#
Real Time Clock Test	*#0782#
Audio Loopback Control	*#0283#
LBS Test Mode	*#3214789650#
GPS Control Menu	*#1575#
RIL Dump Menu	*#745#
Data Create Menu	*#273283*255*3282*#
Proximity Sensor Test Mode	*#0588#
Camera Firmware Update	*#34971539#
Light Sensor Test Mode	*#0589#
WLAN Engineering Mode	*#526#
Debug Dump Menu	*#746#
NAND Flash S/N	*#03#
Software Version Info	*#44336#
System Dump Mode	*#9900#
Data Create SD Card	*#273283*255*663282*#
Data Usage Status	*#3282*727336*#
TSP / TSK firmware update	*#2663#
Remap Shutdown to End Call TSK	*#7594#
Camera Firmware Menu	*#7412365# and *#*#34971539#*#*
WLAN Engineering Mode	*#528#
Melody Test Mode	*#0289#
OTA Update Menu	*#8736364#
Test History	*#07#
HSDPA/HSUPA Control Menu	*#301279#
Quick Test Menu	*#7353#
View Phone Lock Status	*#7465625#
Auto Answer Selection	*#272886#

HTC Secret Codes

Description	Codes
Device information program	#*#4636#*#*
Field Test	*#*#7262626#*#*
HTC Function Test Program	*#*#3424#*#*
Display Software version	*#*#1111#*#*
Display hardware version	*#*#2222#*#*
Wi-Fi Mac Address	*#*#232338#*#*
Bluetooth Mac Address	*#*#232337#*#
GPS Test	*#*#1472365#*#*
GPS Test 2	*#*#1575#*#*
Bluetooth test	*#*#232331#*#*
Display test	*#*#0*#*#*
Touch Screen version	*#*#2663#*#*
Touch Screen Test	*#*#2664#*#*
Debug UI	#*#759#*#*
Factory format	*2767*3855#