Warren Fields has dropped cell phones into a toilet and a big puddle near a parked car, even over the deck of a boat.

The Michigan resident — who owns a mattress store near Detroit with 12 delivery drivers, all of whom use company cell phones — buys a lot of phones. And he doesn't want to pay too much.

Cheap replacement phones are not readily available from major wireless carriers, unless you have insurance or are eligible to extend your contract. Without a promotional subsidy from the carrier, new phones can cost $100 or more.

Fields found a solution online in the growing used cell-phone market, where replacement handsets can be picked up for as low as $20. "I don't care if the phone is scratched and not pretty," he says. "I just need something that has a dial tone and works."

With 200 million people in the United States using cell phones, countless thousands of phones are lost or damaged every day. Savvy entrepreneurs are finding ready customers online seeking alternatives to contracts and full-price phones.

Type "used cell phone" into a search engine and scores of possibilities pop up.

CraytonElectronics.com, Cell phoneshop.net and usedcell phones.com offer online stores for used phones with guarantees and warranties.

While used phones are cheap, the downside is that you're buying someone else's castoff, says Peter Rojas, editor of the tech enthusiast Web site Engadget.

"Anyone who has owned a cell phone knows the lifespans on these things aren't that great," he says. The first thing to go on a used cell phone will be the battery, he says. Replacement cost: around $25.

Crayton Electronics CEO Marc Zuccato says his staff tests all phones before they get resold.

He says his phones aren't always pretty, or up to date, but "the guy who wants the latest and greatest doesn't buy from us," he says. "My consumer just wants a phone that works and isn't willing to pay the carrier a fortune to get it."

Columbus, Ohio, resident Mark Miller lost his Samsung phone at a hockey game. He says that when he visited his local Sprint store, he was told it would cost $180 for a replacement. His other option was to renew his contract for another year, but he didn't want to be locked in.

So he started searching for used phones online at eBay and ended up at Crayton, where he spent $40 for a Samsung 3500, with a charger and new battery. "I'd do it again in a heartbeat," Miller says. "It's not flashy, and a little dated, but I don't care."

USA Today visited Sprint, Cingular, T-Mobile and Verizon stores in the Los Angeles area, seeking a sub-$100 replacement phone with no further contract commitment. Employees at each store suggested we look online at auctioneer eBay and classified ad site Craigslist. With those options, consumers have to be comfortable dealing with private parties, and in the case of Craigslist, arranging to meet in person to arrange the transaction.

In online searches for used phones, many sites pop up that appear to sell used phones but actually don't. Sites like Simply sellular.com, selloldcellphone .com, phoneiscash.com and cash myphone.com buy used phones from the general public via their Web sites, and resell them to brokers, who generally move them overseas.

When shopping for a used cell phone via the Web, the first order of business is making sure it will work with your carrier. Cingular subscribers need to shop for Cingular-compatible phones, ditto for Sprint, Verizon and T-Mobile.

Subscribers to Cingular and T-Mobile service have it the easiest. Those phones store your customer information, phone number and contacts on internal, swappable SIM (subscriber identity module) cards. All you have to do is take the SIM card out, stick it in the new phone and you're in business.

Sprint and Verizon phones require re-activation from a company rep, which can be done over the phone or in person at one of the stores.