I knew that cordless phones could be 900 MHz or 2.4 GHz. At the office I have a 2.4, which I bought with the apparent mistaken perception that it would have greater range. It works in most of the three story building where my office is located, but not in the server room of my client on the third floor, where it would be most useful. Lots of RF in there.
I was unaware that 802.11a wireless was at 5.8 GHz, and thus less likely to interfere with phones and vice-versa.
At any rate, go read Chan’s post. I learned a lot from it, and you may too.