Add a Cordless Phone, but Not Interference

Yesterday a friend called me to explain that his wireless network did not have the range he thought it should have, in his high-rise apartment. He also explained to me that the connection kept dropping now and then. Of course this could be a hardware problem, requiring a replacement of the hardware or a firmware upgrade.
It also could be interference from one of any number of devices – including his cordless phones.

A NY Times readers asked, Our computers are connected to the Internet by a cable modem and a Linksys wireless access point. I want to buy a new cordless phone, but I am worried that it may disrupt the network. Are there cordless phones that use a frequency that will not interfere with the wireless network?
The NY Times answered The most common wireless networks for home users, 802.11b and g, can sometimes interfere with some cordless telephones because they use the 2.4-gigahertz frequency to broadcast signals from the base station to a computer or handset. Other devices like baby monitors or older microwave ovens can also disrupt a wireless network. Although interference from other electronic products may not block the wireless network signal entirely, it can make the network slow and balky. (get the full answer)