iPhone update debuts Tuesday. Why not get cash for your old iPhone?

The iPhone 5 – or maybe iPhone 4S – will emerge at Apple's special unveiling Tuesday. If you're thinking about getting the latest iPhone, you might as well earn some money off your aging model.

With the expected release Tuesday of the next iPhone, some owners of the current version of Apple Inc.'s hit phone won't sit home and grumble. They'll sell, then upgrade.

Smartphones and other tech gear that are rendered obsolete by the latest version, or just get a little old, certainly are far too valuable to stash in a drawer and forget about. In fact, with an iPhone, you might be able to sell it for nearly the price you paid. But you have to know how to play the "recommerce" game to get top dollar.

Recommerce isn't just for iPhones but for many of today's tech gadgets, from BlackBerry phones to Xbox gaming consoles to laptop and tablet computers. Some consumers are seeking cash, while others just want a "green" way to dispose of their electronics.

"The very worst thing you can do from an economic and an ecological perspective is stick it in your drawer and later throw it in your trash," said Joe McKeown, vice president of marketing and communication for phone buyback site, ReCellular.com. "It's the right thing to do for your pocketbook and the environment."

Used iPhones are an extreme case because they are always in high demand.

Like the price of a stock, price quotes for used iPhones fluctuate on websites that buy gadgets from consumers. Prices vary more on product-launch days like Tuesday. The difference Tuesday between selling in the morning and evening can be real money.

"We anticipate this will be the biggest event in recommerce to date," said Kristina Kennedy, spokeswoman for Gazelle.com, which buys used electronics. Shortly after Apple announced Tuesday's news conference about the iPhone, Gazelle's traffic spiked. There was a period where people were locking in a price to sell their old iPhones at the rate of one every 10 seconds on the site, Kennedy said.

Compared with the launch of iPhone 4, traffic at ReCellular.com in recent days is double, McKeown said.

A survey by mobile advertising network InMobi released last week showed that 41 percent of current mobile phone users in North America plan to buy an iPhone 5 — before there was even confirmation an iPhone 5 existed.

"People just want to have the latest and greatest," Kennedy said. "When they're on a plane and the person sits down next to them, they want them to notice they have the iPhone 5, not the iPhone 4. There's sort of a badge of honor that comes for the hard-core Apple enthusiasts with having the newest one."

Many buy-back sites resell used phones — on eBay, for example — although, ReCellular.com buys and sells used phones on its own site. Consumers can check those websites if they're in the market to buy used iPhones.

If you want to sell using a gadget buyback website, resale prices on iPhones are typically high the morning of Apple's announcement of a new model. So, lock in a price by mid-day, Kennedy suggests. "After that, we do expect the pricing to drop very quickly," she said. On Gazelle and some other sites, you can lock in a price and ship the phone weeks later, giving you time to buy your new phone and transfer service to it.

Owners of iPhones might be shocked to know you can sell your phone and get back most of what you paid. That's because U.S. wireless carriers usually sell phones for less than cost and make up for it with the price of the service plan. For example, many consumers paid $299 for their 32-gigabyte iPhone 4, which retails for at least twice that. One buyback site, Cellitused.com, on Monday was offering $232 for one in good condition, and $290 for one in like-new condition, according to price aggregator uSell.com.

Upgraders can use the money to defray the cost of a new iPhone or help pay early termination fees if they will be jumping to a new wireless carrier before their contract expires. Some gadget buyers pay cash, while some store-sponsored buying programs pay in store credit.

Rob Brandenburg, 39, of Chicago is planning to upgrade from his current iPhone 4, which he says seems sluggish and "quirky" lately. "Right now, I'm having a lot of speed issues," he said. Instead of selling his iPhone 4, he'll pass it to his wife and probably sell her previous-generation iPhone, the 3GS, he said.

He said he would probably sell the older iPhone to a friend or use an online marketplace, such as eBay or Craigslist — or maybe he'll just ask around. "I've sold a couple of them just by word-of-mouth," he said.

Here are three primary ways to sell your iPhone or other used tech gear.

– Sell to a gadget buyback website. Selling to one of these sites can be a low-hassle option, but you might not get top dollar. Gazelle.com, for example, concentrates on being simple and fast. After you accept its offer, it will send you a box with prepaid shipping. Or you can go to a FedEx store, and personnel there will package it for free. Usually payment is issued within a week of your device arriving, Gazelle says on its website.

USell.com is an aggregator, searching prices on three different buyback sites. And ReCellular.com is among the oldest sites for selling and buying used phones. It touts 20 years in business and recirculating some 50 million phones.

– Sell it yourself. You're likely to get a higher price for your gadget if you find your own buyer. Often that means using word-of-mouth or such online tools as eBay or Craigslist. But it can be a hassle to create an advertisement, respond to potential buyers and package and ship the item yourself. EBay has an Instant Sale section where it offers fixed payouts via PayPal.

– Retailer buybacks. Some gadget upgraders might prefer to deal with a known retailer. Electronics retailer Best Buy will give cash or store credit for trade-ins. A 32-gigabyte iPhone 4 in good condition yields $181 in cash or $279 as a Best Buy gift card. Amazon.com on Monday was offering $274 for the same trade-in. Its payout comes in the form of an Amazon.com gift card.

A word of caution: before selling, be sure to erase all your private data on such devices as computers and phones. Many devices have an option in their settings to wipe all data and restore the gadget to factory defaults. Some used-gadget buyers also say they will securely erase your data.