Updated

Although the exact release date for the iPhone 5 is yet to be known, many are speculating Apple's next best thing will come to stores in September. That gives you about a month to start saving. If you're willing to trade in your iPhone 4 or 4S, though, you could earn back some of the cash you'll need to purchase this new superphone.

In fact, some trade-in sites are offering up to $455 for Apple's iPhone 4S with 32GB. But which sites offer the best deals, what condition does your iPhone have to be in and, most importantly, what's the catch? We did some investigating into such trade-in sites as Gazelle, NextWorth, BuyBackWorld and BuyMyTronics as well as trade-in programs at Amazon, eBay Instant Sale, Verizon, Best Buy and RadioShack to see how much dough you can collect for your iPhone 4 or 4S.

Although most trade-in services can about a week to pay you (usually via your choice of check or PayPal) for your iPhone, BuyBackWorld issues payment within 48 business hours. Some limitations: Amazon, Verizon, Best Buy and RadioShack's trade-in programs will only pay you via gift cards to their stores or sites. Apple's Recycling Program doesn't offer monetary value for your old iPhone, but if you bring it to an Apple store they'll recycle it for you.

Although Amazon offers up to $415 and eBay Instant Sale offers up to $299 for a 16GB iPhone 4S, we imagine that smartphone would have to be in mint condition to get the full amount. The next best bet for that phone is through Gazelle for $277 with BuyBackWorld coming in a close second at $275. For whatever reason, though, you'll earn more cash for this phone at Gazelle if your carrier is AT&T.

If you upgraded to 32GB in your iPhone 4S, Amazon and eBay claim to reward you with up to $455 and 331, respectively. Again, we doubt you'll get that much cash unless your fingers have barely grazed that phone's display. And Gazelle and BuyBackWorld take the prize again, each offering $300 for this model in good condition. BuyBackWorld offers the same amount across all carriers, but AT&T earns more cash at Gazelle.

It's a bit older, but you can still earn a good amount of cash for your iPhone 4. If you have a 16GB model, Amazon and eBay Instant Sale promise up to $290 and $186, respectively. If you want a sure thing, BuyBackWorld offers $203 on Verizon and $180 on AT&T, and NextWorth promises $170 through AT&T (but only $150 on Verizon).

The 32GB iPhone 4 goes for up to $300 on Amazon and up to $219 on eBay Instant Sale, and the next best thing is $208 for a Verizon model through BuyBackWorld (the AT&T model is worth $180). RadioShack offers up to $183, and Gazelle and NextWorth offer $180 for this model.

Although it'd be nice if we could make sense of these prices, it seems to be somewhat of a random draw. And although BuyBackWorld generally offers the most cash for your iPhone 4 or 4S, deals at Gazelle and NextWorth are also worth checking out.