 All right, so you just upgraded your phone. You want to trade in the old one to maybe make some money or lighten up your monthly bill. So remember this. If you're looking to make some cash by selling an old phone, you have to do two things because your old phone contains all sorts of sensitive data. Think about it. Your credit card numbers, your bank account details, your passwords, maybe some private pictures. And so you want to make sure that all that intel does not fall into the wrong hands.