Technology vendors have long used Earth Day as an excuse to polish their environmental records, but in 2007, many companies are finding they can generate revenue through the practice, the website Computer World reports.

In the past year, PC vendors, including Dell Inc., Hewlett-Packard Co. and Apple Inc., have expanded their programs to take back obsolete computers for free recycling. And beginning in April, Motorola Inc. and Nokia Corp. offered their customers greater incentives to return older cellphones.

This is not just charity work, analysts say. In addition to improving their public relations, those companies can also generate new cash, the website states. 

Some PC vendors earn growing revenue by selling parts, as they see rising global demand for plastics, components, scrap and refurbished PCs, according to a report by David Daoud, an analyst at Framingham, Mass.-based market research company IDC. Some vendors also use take-back programs as a way to convince customers to buy new PCs more often.

According to IDC, one of the biggest challenges for consumers is finding a better way to collect the flood of obsolete hardware.: 7 percent of consumers put their used PCs into municipal recycling; 34 percent donate them; and 35 percent store them in an attic or garage. The corporate world is nearly as bad, recycling only 30 percent of PC assets through official channels, compared with donating 70 percent of them to nonprofit groups and employees.

Last year, that picture started to change, Daoud said. The percentage of recycled PCs rose significantly, as companies cut the number of computers they tossed in the trash and saw a shrink in the demand for donated obsolete technologies.