With most companies releasing mobile devices once a year (or more), and subsidized mobile contracts stubbornly stuck at two years, it can be a tough financial proposition to upgrade yearly. One easy way to generate some cash for The New Hotness is to sell last year's Hotness. To do that, you want to make sure your device is scrubbed clean of all your own data so the next person can start fresh. Here's how to prepare your iOS or Android device for sale.