Nokia has clambered onboard the green bandwagon with three mobile phones that encourage users to unplug the charger from the wall socket when not in use. 

The Finnish giant estimates that two-thirds of the total energy consumed by mobiles is wasted as a result of people leaving the charger idle in a live socket once the phone has been unplugged.

"We want to reduce this waste and are working on reducing to an absolute minimum the amount of energy our chargers use," said Kirsi Sormunen, vice president of environmental affairs at Nokia.

Nokia aims to reduce the amount of electricity a charger consumes while still plugged into the mains, but not the phone, by an additional 50 per cent by 2010.

Nokia phones already have an onscreen alert to say when charging is complete. The new alert appends the words 'Please unplug the charger' and provides an audible beep.

However, the company was unable to say how this would work for the millions of people who charge their phones overnight while asleep.

The alerts will be implemented initially on Nokia's 1200, 1208 and 1650 models, targeting high-volume sales in developing markets like India, China and Latin America.

Nokia said that the new alert will be rolled out across the whole range at a later date.