If you're among those lucky few who are eligible to upgrade to an iPhone 3G S without paying full retail pricing, here's good news: you can sell your old iPhone 3G and walk away with some extra cash.
Let's say you have the 16GB model. A quick check of Craigslist and eBay shows that the going rate for a mint-condition 16GB iPhone 3G is around $400.
Now, it doesn't take a math whiz to figure out that if you buy a 16GB iPhone 3G S for $200, you'll walk away with a $200 profit. Grab the 32GB model and you make $100. Not too shabby, eh?
Of course, with the sudden glut of used iPhones out there, you may have a tough time finding a buyer. If you'd rather not deal with the hassles (and potential wait) of selling to another individual, consider selling to a service.
iPod fix-it shop Rapid Repair, for instance, has an iPhone buyback program that's currently offering $230 for an 8GB iPhone 3G and $270 for the 16GB model. It'll even pick up the cost of shipping.
I also got an online quote from used-gadget buyer NextWorth, which offered about $220 for my 16GB 3G.
Sadly, I'm not eligible for upgrade pricing until 2047, or something ridiculous like that. (Thanks, Apple!) So I haven't been able to put any of these methods to the test. If you have, be sure to leave a comment detailing your experiences.
If you do decide to sell your old iPhone, here's some advice from resident forensics expert Jonathan Zdziarski: 1) Pull the SIM card. The new owner won't be able to use it anyway. 2) Erase the phone by tapping your way into Settings > General > Reset > Erase All Content and Settings. Make sure to keep the phone plugged in, as this process can take a couple hours to complete.