Don't know what to do with those old cellular phones?

Most people don't.

The average lifespan of a cell phone is about 18 months, according to industry statistics. Users upgrade that often, or change service providers and buy new cell phones.

A recent survey conducted by the nonprofit Rechargeable Battery Recycling Corp. found that more than 56 percent of cell phone users surveyed still have their old cell phones somewhere. Only 2.3 percent recycled them, and more than 70 percent were unaware they could be recycled.

"With 150 million [U.S.] cell phone subscribers and every 18 months they're getting new phones, there are millions of cell phones every month that go inactive," says James Mosieur, CEO of RMS Communications Group in Ocala, Fla. Two years ago, he founded CellForCash.com, one of several Web-based businesses that buy back used cell phones from consumers.

"Most people don't realize there could be value in that old phone," says Mosieur.

CellForCash.com collects 8,000 to 10,000 used cell phones a month, he says. Eighty-five percent of them come from consumers who visit the Web site and find their used cell phones among the 200 to 250 recyclable models listed. They fill out the online form to receive postage-paid boxes for shipping. When the company receives the phone, it sends the check.

How much depends on the make and model. Customers get $5 for a Nokia 5165, one of the oldest models CellForCash.com accepts. An NEC 523 earns $43. A Panasonic GU87 goes for $60. "We have phones out there worth three bucks, but we also have phones valued at over $100," says Mosieur.

He resells most of the phones in South America.

So does Robert Newton, owner and president of Old Cell Phone Co. in Port St. Lucie, Fla. He buys back 30,000 used cell phones a month.

"The used cellular phone market down there is huge," says Newton, explaining that cell phone technology in Third World countries trends a step behind technology here, so as U.S. consumers go from digital cell phones to GSM technology, South Americans go from analog to digital.

Newton says most cell phones of the past five years, or "85 percent of the cell phones out there right now," are resalable. The average price his company pays is $12.

But reselling old cell phones isn't just about money. Recent studies by the University of Florida found that millions of old cell phones dumped into landfills could leach dangerous levels of lead and toxins such as brominates from flame retardants in the plastic housing and arsenic and nickel from their circuit boards into soil and ground water, causing an environmental hazard.

"Potentially there could be 100 to 200 million cell phones that end up in landfills," says Mosieur.

Legislators in several states, including Maryland, Virginia, New York and California, have proposed or passed electronics disposal bills that make disposing of old cell phones in landfills illegal or set up cell phone recycling programs. One California bill would require cell-phone retailers to accept and recycle used phones.

A few retailers, such as AT&T Wireless, already do. And several charities now offer nationwide drop-off sites. Verizon's HopeLine program collects used phones at any Verizon Wireless retail store to help domestic-abuse victim groups.

But, Mosieur says, none of the retailers or charities gives consumers cash.

"People aren't going to get rich for selling their old phone," he says. "But rather than give your phone to your son or daughter to play with, why not give them the $5 to put in their piggy bank. There are a lot of better uses for these old phones."

Got questions? A consumer complaint? A helpful tip? E-mail details to oldenburgd@washpost.com or write Don Oldenburg, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.