From what ive read (never really took the time to test it to see how harshly it interfered) the 2.4ghz cordless phones do tend to interfere with many wireless networks. Especially when its near the router, or an individual adapter trying to connect to the network. Makes sense seeing how they are running at the same frequency. But like I said above I havent tried it to see if it would just cause some issues or if its bad enough to bring a whole network to its knees.
Easy way to fix it is to upgrade the phone to a 5.8ghz cordless phone. Better sound quality anyways =)