Need a little help with frequencies. Does IEEE 802.15.4 radio channels 11 through 26 possibly interfer with 802.11b since they both use 2.4GHz?
Yes, interference is not based on the protocol used, it is only based on the frequency of the transmission. So regardless of the source, anything in the 2.4GHz space will interfere with WiFi devices. That includes BlueTooth, Microwaves, and cordless phones.
BlueTooth can be very harmful to WiFi since it uses almost the entire band, but it fortunately does so at very little power, so interference is generally limited.