To do a full phone formatting on your phone as steps below;

1. Make sure you have at least 3/4 charge of battery power left.
2. Backup your contacts list and personal files to MMC memory card.
3. Switch-off your phone.
4. Press and hold these 3 keys; Green dial key, * (star key) and no. 3 key and then press the power on/off to switch on the phone.

Remember, do not let go all of the keys, hold until you see a formatting word screen show!

5. After a few minutes when the full phone formatting completed, your phone will be back to original system and factory setttings.

Normal Reset *#7780# : Restores ini files from rom but preserves user data (photos, 3rd party apps etc)
Hard Reset *#7370# : This reformats completely the C: drive. All applications and files stored on this drive will be lost and clean default files will be rewritten.