Another thing to keep in mind is that there are different types of 2.4 GHz phones (even among digital models). Older ones, that were designed back before everyone had a LinkSys in the closet, will camp on about a third of the 802.11 spectrum, and essentially black out network comms in that band. Many of the newer models will play nicely with wireless routers, by negotiating with their base station to use a channel that's not otherwise in use.
I have two different 2.4GHz phones in my house; the older one always takes the network down when we use it, and the newer one never interferes with the network at all.
Since BrokenKid's computer is on the wlan, judicious use of the old phone can sometimes terminate endless IM conversations between her and her friends (plus provide hours of amusement). Of course, the cron job in the server that cuts off her interwebs at 10pm does a pretty good job of that, too.
-BP