By Jonathan Marshall

“Let your fingers do the walking” was one of the last century’s greatest advertising slogans, created to promote the Yellow Pages. Today it applies even better to smart phones, those ubiquitous appliances that help us book flights, navigate streets, check stock prices, follow friends, and even get real work done with a few flicks of your finger.

Smart phones also can help you lead a greener life if you load them with the right applications. A good place to start is the Sierra Club’s recent list of Top 10 Smartphone Apps for an Eco-Friendly Home and Lifestyle.  Most of the apps are free and the rest cost as little as 99 cents, a small enough investment in a more sustainable world.

They’ll help you estimate your carbon footprint, find recycling centers and farmers markets, alert you when battery-powered devices finish charging so you don’t waste energy, and choose sustainable seafood options as markets and restaurants.

One of its highly rated sites is GoodGuide, founded by a UC Berkeley environmental policy expert, whose scientific experts rate products and companies on their health, environmental and social performance.

Another is iViro, which helps users conduct a full home energy analysis and determine the best places to make energy-saving changes, including estimates of yearly savings and payback periods.

Energy-saving applications for smart phones are multiplying these days thanks to the Green Button initiative launched by the White House and backed by PG&E. PG&E and other participating utilities now let customers pass home energy usage data to third-party applications, which provide help analytical tools.

But what about smart phones themselves—how green are they? It turns out that the Electric Power Research Institute produced a report on just that question in June.

It found that an Apple iPhone 3G consumes only about 2.2 kilowatt-hours of electricity over the course of an entire year, at a cost of about a quarter. That’s less energy than a single 100-watt light bulb would draw over 24 hours.

So keep playing Angry Birds on your smart phone with a good conscience. Just be sure to consult one of those green apps from time to time to keep your lifestyle on a sustainable path.

Email Jonathan Marshall at jonathan.marshall@pge.com.