Glenn
They are correct in the interference thing. Those 2.4 Ghz phones will interrupt with the wireless signal. But they will only interrupt when the phone is in use, where the base station is talking to the remotes or remote to remote.
Changing channels will reduce the level of interference but will not get rid of it entirely. As with the phones as well as default of the router, they cycle channels to find the best one. To change the router, you will need to look at the manual for it. for example, some Linksys routers have a wep page where in the general settings you can set which channel to use. And make sure to look to fix it at a channel and to unselect automatic channel select or channel optimization.
Again, this many times will not reduce it enough. What some of my friends have done is to go out and buy the 5.4 Ghz phones.