NOKIA CODES
There are some useful secret codes for Nokia S60 phones to get system information. Some may be known to you some may be not.
1. *#0000# - Display the software version, the date whenthe software was built and the phone model. In some cases, the phone model is not the one usedby marketing. It is the internal model used inside Nokia. For example, RM-36 is the internal name of Nokia 6680.
2. *#06# - Display IMEI (International Mobile Equipment Identify) of your phone.
3. *#2820# (*#BTA0#) - Display the Bluetooth device address of your phone.
4. *#62209526# (*#MAC0WLAN) - Display the MAC address of the WLAN adapter. This is available only in the newer devices that support WLAN
5. *#7370# (*#RES0#)- Reset your phone to the default factory settings. Usually you will need this code when you want to reset your phone back to thesame condition when you got it for the first time. When the phone ask for security code, thedefault one is12345.
Warning: Before you do reset the phone, make sure that you don't have important data. Your data on the phone memory will be lost once you reset it.
6. *#92702689# (*#war0anty#) -Display the life timer information of your S60 phone, i.e. the total time of phone call (in minutes). Some users have asked how to reset this timer; as far as I know the only way to reset it isby flashing the phone.
7. *#7780# (*#rst0*) - 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.
8.Format-There is another key combination which is used to format the phone. It is useful in some cases, for example when the phone cannot reboot. The trick is by switching off the phone then pressing and holding the Call key (Green key) + * key+ 3 key + power button till you see the timezone menu and thenrelease them.
Formatting should be done only in extreme situations.

JUST FOLLOW SIMPLE STEPS
1. Create any new folder or you can use any existing folder that is to be hidden.
2. Rename the folder to any name but with the extension of .jad like if I want to hide my images folder then I will name it as IMG.jad
3. Now create a new folder with the same name in the same directory but with the extension of .jar So, I would create the folder with the name IMG.jar
4. And thats it!! My orignal images folder which has been renamed with .jad gets hidden and only folder with.jar extension is visible which is empty.So,my data is protected/hidden from unwanted eyes.

Note :This trick can be used for any JAVA phone from Nokia,Samsung,Motorola,LG or any other company.
To unhide the orignal folder you have to remove the .jar extension from the new folder and your orignal folder with all the files and with .jad will become visible.