Go to Settings-->Options„łSecurity Options-->General Settings and then click the trackball (or on the 8110 click the menu button) and select Wipe Handheld.

There is then a comforting series of confirmations that prompt you to verify that yes, in fact, you really want to strip everything off. It's pretty unlikely you're going to wipe the device by accident.

Do note that wiping it cancel any service you have set-up. The actual process of clearing it takes a few minutes and you'll be cautioned not to remove the battery until it's complete.

If the finality of a wipe is too much to bear, you can always resort to just burying the device in the bottom of a drawerˇXbut do cancel the service so you donˇ¦t continue paying for its retirement.