Your cellphone contains memory, which is kinda like a hard drive, so to speak. When you are letting go, selling or loaning your old model in favour of a new one, be careful. You think your deleting all of your personal or confidential information from your cellphone, like telephone numbers, emails, pictures etc, but according to this article on Personal Finance Advice, your not.

Think about the transactions you might have made by using your cellphone. Your banking records, passwords can all be vulnerable. All private information that can be retrieved to create identity fraud and lead to financial ruin. The article does provide some good tips on how to permanently avoid these risks associated with old cellphones. Be cautious, you never know where your cellphone might end up, or with whom.