replace your phones with DECT phones...
only buy pansaonic..
stay away from uniden and vtech...
check your line with a corded phone to ensure that the static is not on the line or jack... and if there is static at the jack, check the NID with the corded phone to determine if the static is inside or outside of your home... if outside call your local telephone provider to make the repairs... if inside and you have wire maintenance then the phone company can come and make the repairs free, otherwise they will charge you - or you can do it yourself, or have someone else do it...
DECT phones operate on 1.9Ghz which is an unlicenced radio spectrum set aside by the FCC for cordless telephone devices only... so other devices should not interfere... also with RF the lower the frequency the further the range, so they will provide better range than 2.4 and 5.8Ghz phones...
2.4Ghz phones operate within the same frequencies as many consumer electronic devices - wifi, cordless intercoms, cordless baby monitors, cordless video security cameras, microwave ovens..... etc..
placement of the main base - that connects to the dial tone, is also important.. you want to locate the main base in a location centered on the area you are attempting to cover with the cordless phone... keep in mind that physical obstructions (doors, floors, etc) can block or reduce the signal level and range of the phones.....