How to Clear/Delete all your Address/Calendar items at once

From BlackBerryFAQ

If you are having errors in your Calendar or Address Book on your BlackBerry, and you wish to delete the entire Calendar (or Address Book) database on your BlackBerry, follow the directions below. Make certain you have a good copy of your Calendar or Contacts elsewhere, as this procedure will complete delete ALL Calendar entries and/or Address Book entries on your BlackBerry.

1. Open Desktop Manager

on your PC.

2. Open up Backup/Restore > Advanced.

3. From Advanced you'll see a split pane screen. The left pain is what is going to be backed up from your device and the right is a list of the currently existing databases.

3. Highlight on the right side your Address Book database (or your Calendar database) and click the arrow in the middle pointing to the left. This will copy the information over and prepare it for back-up.

4. Once the back-up has completed, hit the Clear button at the bottom to erase and clean out the entire address book database (or Calendar database).

5. After it's finished, it will ask you if you want to save the back-up you've created, say yes and check the device to make sure the address book has properly cleared out. Now, resync the necessary contact information and you should be set to go.