Problems with wireless net timing out

I have a Dell D600 laptop connecting to a 2Wire wireless modem.
However, when I connect to the network/internet to connection is only
active for about 5 minutes. If I bring up the Wireless Network
Connection Status, it says that my signal strength is max (5 green
bars). Then I disable and enable the Wireless Network Connection, I am
good for another 5 minutes. what could be causing this problem? Someone
mentioned having a wireless phone could cause problems with wireless
networks (I have an old AT&T 900Mhz cordless phone)

Any comments/suggestions appreciated