The good news: You've got plenty of options, starting with the most obvious choice--turn that old iPhone into a slightly used, slightly thicker iPod touch. Your calling capabilities and 3G/EDGE connectivity may have moved on to the iPhone 4S, but that old phone of yours can still connect to Wi-Fi and still run iOS apps. (And if you upgrade to next week, you'll add even more capabilities to your supposedly defunct phone.) Should anything go wrong with your new phone, it never hurts to have a backup in easy reach.

But if you're ready to let go of that iPhone 4 or iPhone 3GS, here are a few more options worth considering.

Apple features a Reuse and Recycling Program; earlier this week, the program was offering to for a gently used, top-of-the-line iPhone 4. (That payoff--which comes in the form of an Apple gift card, and not cold, hard cash--drops off for phones with scuffs, scratches, and water damage.)

Verizon also that lets you get an online appraisal on your current phone; the company will pay you that value in the form of a Verizon gift card. AT&T, meanwhile, has its own program--that company asks you to bring your old phone to one of its stores.