Cordless phones use between 2 and 3 watts in both active and standby modes. About 60% of cordless phone energy use occurs during standby time.
If you still want the convenience of a Cordless Phone, consider just having one or two for your home, and get corded versions for rooms you aren't in as much. The energy savings will add up. Make sure the Cordless Phone you do get is Energy Star-rated, indicating high energy efficiency.
Also Corded Phones last longer. Battery operated Cordless Phones needed replacing every couple of years because the batteries go dead and finding a replacement batteries always seems to be a challenge.
In the ideal home we would have traditional land line Corded Phones for local only calling and 911 emergencies and Cordless Phones in your office and the kitchen with an interface through your computer to connect to VOIP to call anywhere in the world at a fixed rate. Your Wireless Cellular Phone would connect to the VOIP while you are at home or at the office or near a Kiosk through wi-FI and VOIP and through Wireless Cellular Phone towers when the WI-Fi was not available
