Even more important than cash in hand, data security should be your top concern when offloading an old iPhone used for work, so wipe that handset clean. If you don't, you're essentially handing your contacts, usernames and passwords, e-mails with clients and co-workers, Web browsing history, and saved meeting locations from Google Maps to a stranger.

The iPhone 2.0 operating system introduced an built to overwrite deleted data several times. It could take several hours, based on the phone's storage capacity, but with a simple point-and-click function. If you don't have the iPhone in hand but have a MobileMe account, check out the .

If your device runs an earlier operating system, wiping your personal data may be less easy and thorough. There are several steps required .

You can purchase a program such as to wipe old iPhones before you resell them. For companies with tight security issues, this might be a better option.