If 5 percent of U.S. households chose one corded phone over the cordless model, the energy savings would total 140 million kilowatt hours annually -- enough talk time to keep 130,000 teens' phone lines busy for every waking hour of the summer.
Do away with cordless.
If you need to buy a new phone for a bedroom or home office, consider buying one with a cord. You'll save about 28 kwh of energy per phone annually. Standard corded phones consume little energy, while cordless units draw constant power during charging and standby modes.
(taken from bankrate)