(Tested in Nokia 3230)
In order to enter theses codes, the phone must be in the idle screen not in any of the menu screens. The idle screen is where you see the operator name, date, time, battery level, signal strength.
*#7370# – Resets your phone to the default factory settings. Usually you will need this code when you want to reset your phone back to the same condition when you got it for the first time. When the phone asks for security code, the default one is 12345 unless you have specified one yourself.
Warning: Before you do reset the phone, make sure that you don’t have important data and that you know the security code for your phone. Make sure you have at least 3/4 charge of battery power left. Your data on the phone memory will be lost once you reset it.
*#7780# – This will soft reset your phone. It is different from *#7370# because all data, like contacts, calendar and notes, are not removed. It will only reset the phone settings, such as profiles, themes and shortcuts. The default lock code is 12345.