There will come a day when you and your BlackBerry part ways. Though that stalwart piece of technology has served honorably, there are always something new upon the horizon. On that sad, sad day, there will be many heartfelt speeches about all the good times together. Tears well up as you check your email one... last... time...
Who am I fooling? You're going to be too excited about your new BlackBerry to really care about the old one! Once you've completed the Device Switch, your old phone is next to forgotten. Take a moment, though, to consider what will happen to that BlackBerry. Will it need to be returned to the warranty or insurance center? Will you donate your phone to a worthy charity? Passed down to a friend or family member? Thrown in the garbage? (not recommended)
Before you do, make sure to remove your personal data from the device. If you don't wipe the data from your BlackBerry, you're basically saying, "Here's all my information. I want to get my identity stolen by the random person who gets this phone!" Don't give away your life story; prepare your BlackBerry for its next life by removing all of your data, leaving your old BlackBerry a tabula rasa for its next owner.
This process is irreversible. Once it has started, it cannot be stopped without at least some data loss and the potential of damaging the operating system. Make sure you have successfully backed up the data on your device. You have a number of options to choose from: BlackBerry Desktop Software, BlackBerry Protect, and even BlackBerry Swiss Army Knife can be of assistance. In whatever way you choose to go about it, back up your data.
Removing the data on your BlackBerry is not a difficult procedure, but it's not as simple as click, click, click, either. You have to want it; there's no excuse for "accidentally" wiping the data from your device. Open the options menu; the icon usually looks like a wrench. From there, select Security (Security Options in OS5 and below) and then Security Wipe.
You'll have the option to delete data, applications, and any files on your Media Card. My recommendation would be to delete the data and applications and keep your memory card for your next BlackBerry. Otherwise, select all three options. At the bottom, you'll need to type "blackberry." This is the final check to make absolutely certain you want to delete, wipe, and remove all of your personal data.
Using the Desktop Manager offers a bit more control over the deleting processes, but nevertheless accomplishes the same function. Attach your BlackBerry via USB and start BlackBerry Desktop Software. Once your device has connected, open the Device menu and choose Delete Data... In the next window, you can select to delete all or only some of your data. You're also prompted to complete a backup before deleting. As before, you will be asked to confirm your data deletion.
It is possible to wipe your BlackBerry completely using BlackBerry Swiss Army Knife. This removes the operating system as well; the phone will be useless. If you are returning your phone to a warranty or insurance claim center, this may be acceptable. If you plan on donating, selling, or giving away your BlackBerry, completely wiping the device would be an irresponsible action to take. Put an OS back on that phone before you pass it on.
When parting with your BlackBerry, wiping the personal data from the device is the smart thing to do. Protect yourself from strangers reading your email, thieves finding your passwords, and grandma watching your videos.
BlackBerry 101: How to switch devices
BlackBerry First Steps: Operating systems - official, leaked, and unofficial
BlackBerry 302: A complete wipe and clean install of your BlackBerry OS
BlackBerry 101: How to Reload the Operating System on a Nuked or Bricked BlackBerry