You still can without effecting you warranty or any other plan, as long as you restore it to factory settings when you turn it in. Though my warranty still worked even though I traded my old one *popping screen* in and it still had a jailbreak on it. But I would wipe it before you trade not only to be safe, but also to get all your stuff off that phone. I got a refurbished iPhone 6 at first, and it had a bunch of some dude and his family's pictures on it with angry birds lol. Just be smart about it
