http://blog.didierstevens.com/2008/11/23/quickpost-wifi-availability/

"A WiFi camera, operating on channel 1, is streaming video. When I switch on an analogue, wireless babycam, you see a strong signal appearing near channel 9 (watch the SPECTRAL VIEW of the Wi-Spy spectrum analyzer, e.g. the window in the upper-left corner). After some time, I switch the babycam to a channel near channel 1 of the WiFi camera. Now the transmission of the babycam jams the transmission of the WiFi camera, and we lose connectivity.

Powering off the babycam restores the WiFi connection."

The blog entry includes a link to a video demonstrating the attack, illustrating the danger and ease of a layer 1 attacks.

Here's an article discussing interference from some of these devices:

http://www.informit.com/guides/content.aspx?g=security&seqNum=83

I have seen this also in apartment complexes with cordless phones, Wifi routers, Wireless video, Wii controllers (upto 4 per systems), microwaves, it is crazy the number of devices in 2.4Mhz. The alternative could be to use some of the older 802.11A routers and NICs since it's at 5Ghz. or you could get a cordless phone at 900hz, 2.4Mhz, or 5Mhz. There is not alot of RF spectrum for consumer devices and the more things we get that are wireless the more competition you will see for the RF frequencies.

Brian

Ran across a design for a portable RF jammer today:

http://www.ladyada.net/make/wavebubble/

Might be fun  Also might be illegal, depending on where you live.