It may happens that a program corrupts the C: drive of your phone. In such case, some data can be lost of course but, more annoying, some applications may not work or work only partially,...

Series 60

On a Series 60 v1 based phone (N-Gage, 3650, 7650), two key sequences will allow to restore your phone to a cleaner state:

  Normal Reset (*#7780#) : Restores ini files from rom but preserves user data (photos, 3rd party apps etc)

  Deep 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.

In both case, the phone will ask you a confirmation and you will have to enter a security code (12345 by default).

Files and applications stored on E: drive are not be affected by these sequences.

On newer Series 60 phones (6600/6620/7610), the sequence is slightly different:
  power the phone off,
  press and keep down the keeys green/talk + ’3’ + ’*’, - power on the phone.
  release the keys when the formatting starts.

UIQ

Reformat is also possible on UIQ phones. Just after boot, when the phone waits for the PIN entry, enter the following :
  enter 000, to go into emergency dialing
  then using the jogdial and the keyboard, enter the following sequence:

UP *  DOWN  DOWN  *  DOWN  *

This should bring up a secret service menu with three choices:
  Informations: to access various information like software versions, IMEI, Simlock status and speech codecs supported
  Tests Service: various function to test your phone hardware
  Service function: to completely reformat and reset your phone.