This kind of thing is real problem with non-computer devices. Upgrading to WPA (especially WPA2) will fix the phone but could break other devices (old laptops, TiVo's etc). Another solution is to give up on encryption, especially since WEP isn't really encryption. Almost all routers support MAC filtering, and most support "internet-only" connections, This way you can let any device on your wireless that you know about, and let polite people know they shouldn't connect. Hackers and jerks (not always the same people) can still spoof MAC addresses but that is what "internet-only" is for: you are not exposing your local network over wireless.
Obviously this setup won't work for everyone but it has worked for me in the past, and I might do it again if I get even one more device that can't talk WPA2