If you have ever tried to change programming or applications settings in your Blackberry and ended up nearly breaking the Blackberry instead, you may need to restore the Blackberry to factory default settings. Instead of requiring you to reload the OS, your Blackberry comes with the option to “wipe” the handheld device using the “Wipe Handheld” option. This is not a well-known feature, but is useful when you need to restore your Blackberry to factory default setting because you changed one too features and found your Blackberry becoming unstable. Using the “Wipe Handheld” command will delete ALL data from your Blackberry, so this should be used only in emergencies, when you purposely want to clear any sensitive data from your phone, or when a factory reset of your Blackberry is in order. This is especially useful when you need to return a Blackberry to your employer, but want to eliminate any personal information stored on it, such as messages, contact information, images, or data from third-party applications.

Here is How To Reset A BlackBerry To Factory Defaults:

To start deleting all the data on your Blackberry, click the Options icon on your BlackBerry home screen.
Then, select Security Options
Next, choose General Settings.
When the General Settings screen appears, hit your BlackBerry Menu key, and then choose the Wipe Handheld option.

You will then see a dialogue box appear to warn you that you’re about to initiate a full device wipe. At this point you need to confirm the reset to Blackberry default settings. You’re also given the choice of including all third-party applications and related data in the wipe. You can choose to keep third-party app information on your BlackBerry, but if you want to delete all the data on your BlackBerry smartphone, click the checkbox to delete third party apps.
Another dialogue box will then appear asking you to type the password BlackBerry, or your business-assigned security password. This will then start the deletion process.