Master Resetting Via the Settings Menu:

WARNING! Master resetting your device will return your handset to original factory settings. In the process, personal data that is stored on the device's internal storage will be deleted! Create backups if necessary, before proceeding. Note: master resetting will not delete data stored on the SD Card or the SIM Card.

To perform a software master reset:

  1. Make sure you have backed up any data that you don't want to lose
  2. While on the home screen, select "Menu"
  3. Scroll to and select "Settings" > "Security Settings" > "Master Reset"
  4. Go to "Master Restore"
  5. Select "OK"
  6. Type in "000000" (six zeroes)
  7. Select "OK"

Master Resetting Using Hardware Keys:

Assuming that your phone is unresponsive, locked, frozen or crashes a lot and you can't perform a master reset via the settings menu, then you can reset your device using hardware keys. WARNING! As before, this method will erase any data stored on your phone's internal storage, but data saved on the SD and SIM cards will not be affected.

To perform a hardware master reset:

  1. Back up your data if possible / necessary
  2. Turn off your phone by pressing and holding the "End call" key
  3. Remove the back cover and remove the battery as well as the SIM card
  4. Wait for a few seconds, and then reinstall the SIM card and battery, then refit the back cover
  5. Press and hold the "Pound" key (#) and the red "End" key until a menu screen appears
  6. Select the green "Check mark"
  7. Your phone will now reset to factory settings

See More: T-Mobile 768: Master Reset (via Software and Hardware)