The good news for the environment is that U.S. consumers who bought new mobile handsets in the fourth quarter of 2007 recycled their old phones at double the rate that they did in the third quarter.

The bad news for the environment is that even after the rate nearly doubled, only 9.4 percent of those consumers took the recycling option in the fourth quarter, according to market research frim iSuppli.

More U.S. consumers were motivated to recycle their handsets by the rising awareness of green issues when it comes to disposal of electronic waste, said Greg Sheppard, chief development officer for iSuppli.

More than one third of all old handsets, he noted, were stored away in the fourth quarter of 2007, and now are collecting dust in closets throughout America.

Consumers keep their old phones because they perceive them to have some residual value. However, all too often, those handsets end up in the trash when spring cleaning comes.

The next most common fate for old mobile handsets in the fourth quarter was to be given away to family or friends. Over 15 percent of U.S. consumers gave away their old mobile handsets in this fashion in the fourth quarter. Another 8.5 percent of consumers donated their handsets to charities.

Simply throwing away a mobile handset is not an environmentally responsible action, Sheppard added.

Mobile handsets include hazardous materials, including mercury and lead. The U.S. Environmental Protection Agency (EPA) estimates Americans discard 125 million phones each year, creating 65,000 tons of waste. All this toxic waste can pollute air and groundwater.

Another 5.7 percent said they retuned their old phones to the retailers where they originally bought them.