For WP8:
POWER OFF THE PHONE FIRST
Press the POWER button until it vibrates then release the POWER button.
QUICKLY press and hold the VOLUME DOWN button until an EXCLAMATION MARK is displayed/shown.
Press the magic buttons in order: VOLUME UP, VOLUME DOWN, POWER and VOLUME DOWN quickly.
Wait until TWO rolling GEARS appears, this means that setting to FACTORY DEFAULTS is being initiated.
Phone will restart but will take time just be patient.
All done. Now setup your phone as if it is BRAND NEW!
