I can see with "show controllers dot11radio 0" the channel which the cisco accesspoint is currently using. But is it possible that I can see which channels are taken from other 802.11b/g devices from the from the perspective of the cisco accesspoint?
You can perform a carrier busy test to check the radio activity on bridge channels.
In privileged EXEC mode, enter this command to perform a carrier busy test:
dot11 interface-number carrier busy
Use the show dot11 carrier busy command to re-display the carrier busy test results.