It's common knowledge that a brand new car loses value the second you drive it off the lot. The same can be said for your iPhone, or for that matter, any smartphone. It's especially true when a new version of an expensive phone is about to be released.\n\tApple is expected to launch the next generation\u00a0iPhone in September,\u00a0so the value of the iPhone in your pocket is already dropping. And as launch day gets closer, your device loses more and more value. Nextworth, a company that buys and sells smartphones, plotted the price of used iPhones on eBay. Check out Nextworth's findings below.\n\tAs expected, the oldest version lost the most value. Different models (16GB, 32GB or 64GB) of the same phone cost different amounts, but the decrease in value is roughly the same. Nextworth determined the average selling price of all models of used iPhone 4S devices as the iPhone 5 was initially rumored and then launched. A phone that sold for $399 in June of 2012 was worth just $321 in January of 2013. In the same time frame, the average value of the iPhone 4 plunged from $309 to $238.\n\tThe lesson is clear: If you're planning to sell your iPhone, you should sell it now to get the best price, according to Nextworth\u2019s Jeff Trachsel. \u00a0But if you sell your iPhone now, and the latest one doesn\u2019t come out until the fall, what do you use for a phone until you can get the new one?\n\tBoth Nextworth and a competitor, Gazelle.com, have answers. \u00a0If you agree to sell your phone today, both companies will honor the current price for 30 days. At the moment, both sites will pay $210 for an AT&T 16GB iPhone 4S in good condition.\n\tA quick eBay search reveals a range of prices for used iPhones, but in general you can probably get more on the auction site than you can from Nextworth or Gazelle. Of course, you lose your phone as soon as you sell it on eBay, and you have to deal with shipping and money collection.\n\tIt\u2019s also possible that iPhone value will decrease even faster during this refresh cycle than it has in the past, which would make locking in a good price now a smart move. And if for some reason you no longer want the new iPhone after it is released, you can simply cancel your deal with Nextworth or Gazelle and hold on to what you\u2019ve got.