At Amazon, trade in your "like new" Apple iPhone 3/3GS, 4/4S, and 5, and get up to a $377 credit. (The value of your trade-in is based on the condition of your phone. Once your trade-in is complete, the credit will be applied to your Amazon account.) That's the best trade-in credit offer we've seen on iPhones at Amazon since last fall when we saw up to a $500 credit for select models. This offer applies to unlocked phones as well as phones from carriers such as Verizon, AT&T, and Sprint. Click here to learn more about the Amazon trade-in program.