When learning about and playing with your new smartphone, did you ever stop to think about what to do with the old one? Throw it out? Give it away? You weren’t planning on using it ever again, after all, and it was just going to be a high-tech paperweight. While it may be too late for the phone you replaced years ago, it’s a good thing to know that you can actually sell your old phone. And not for pennies, either. But for real money.