Wi-Fi Interference is a Growing Problem

Wi-Fi interference causes slowdowns and disconnections. From Wired.com:

Got Interference? Data-Crowding Problems Loom for Wi-Fi

Interference on wireless networks will likely get worse before it gets better. Sometimes, the most egregious offenders aren't nearby residential networks or municipal Wi-Fi grids, but the myriad electronic devices in people's homes. Poorly shielded microwave ovens leak radio waves tuned to 2.45 GHz, the resonant frequency of water. Many cordless phones operate in the 2.4-GHz band as well. Wireless keyboards, Bluetooth devices, wireless security cameras and baby monitors can all interfere with a Wi-Fi network.

First step: check to see if your wireless phone uses the 2.4 GHz band. If so, replace it. Most new phones use 5.8 GHz now.