First of all i will give an example so that you can understand my speech here
For privacy between you keep passwords on your mobile, but later on you forgot what the password is so you generally go to mobile service center and ask them reveal my password they will not reveal your password but they will reset your mobile to factory setting(which means when you buy a new mobile it has only operating system installed nothing more than that right).
I will give you some numbers now you will have to just dial them. Then this will restore your factory setting.
FOR NOKIA LATEST MOBILE PHONES(I have tested some of them for my personal use they were working perfect).
These are all hidden Nokia Settings.
Code ---- Action
*#7780#----To restore the factory settings of mobile set
*#3283#----To verify the set Manufacturing date
*#746025625#----To stop the sim clock
*#67705646#----Use to delete the operator logo
*#73#----Use to reset game scores and phone timers
*#0000#----Use to display the mobile software version
*#06#----To display the IMEI Number of the mobile
*#92702689#----To display the mobile warranty related settings (Serial no, Made,
Purchasing date, Repaired date, Life time).
*#7760#----To display the Production serial number
*#bta0#----Use to display Bluetooth MAC address
*#9999#----Use to display the mobile software version
*#147#----If you are using Vodafone then this code will help you show the last call detail
*#2640#----To display the mobile security code
*#7328748263373738#----Apply to resets the set default security code
*#43#----To verify the call waiting status
*#2820#----To verify the Bluetooth information
*#7370#----To format the mobile phone memory
*#delset#----To delete the GPRS AND EMAIL settings
#pw+1234567890+1#----To display the lock status of mobile set
#pw+1234567890+4#----To display the lock status of your SIM
FOR SAMSUNG LATEST MOBILE PHONES(I use samsung mobile tested some of them working perfect)
Code ---- Action
*2767*3855#-----Reset mobile setting.
*#9999#----Use to display the mobile software version
#*3849#----Use to reboot the Samsung handsets
*#06#----To display the IMEI Number of the mobile
#*2558#----To on/off the mobile time
#*7337#----Use to unlock the latest Samsung set
#*4760#----Use to activate and deactivate the GSM features
*#9998*246#----To verify the memory and battery information
*#7465625#----To verify the Lock status of mobile
*#0001#----To display the Serial Number of the mobile
*2767*637#----Use to unlock the mobile code
*#8999*636#----To display the storage capacity of the mobile
#*2562#----Use to reboot the Samsung handsets
*#8999*667#----Use to run the mobile in Debug mode
*2767*226372#----To fine-tune the camera settings
*#8999*778#----Use to display the information about mobile SIM card
*2767*637#----Use to unlock the mobile code
*7465625*28638#----Use to make active the Network Lock
#*#8377466#----To display the hardware version
*7465625*746*Code#----Use to make active the SIM card lock
*#pw+15853649247w#----Use to unlock the mobile code without SIM card
#*3888#----To verify the Bluetooth information
*#9998*627837793#----Uses to get extra parameter for unlock mobile settings
#7465625*28638#----Use to unlock the Network Lock
#*7983# Voltage---- Use to regulate Frequency or Voltage
#7465625*746*Code#----Use to unlock the SIM card lock
#*2834#----Use to reset the handsfree options
#*5376#----To delete all SMS in one command
*#4777*8665#----Use to explore the GPSR tool list
#*2474#----To verify the charging duration
*2767*688#----Use to readjust the mobile TV options
Hope this article will help you a lot guys, many of them are not working.