Active, electronic cancellation is more difficult for a mike than for a headphone. As described above, mikes usually use mechanical cancellation based on direction: the "good" signal (your voice) comes from mostly one direction, while the "bad" signal (noise) frequently comes from all directions. Here's why electronic cancellation is hard: With headphones, the "good" signal is already in electronic form, coming from the radio. The circuit can listen to what's in the headset, electronically subtract the good signal, then send a phase-inverted signal to cancel everything but the good signal. (You might notice that noise, like static, which is already present with the radio signal, will not be cleaned up by this technique.) With the mike, the electronics doesn't have an electrical copy of the good signal, just the good and the bad, combined. Now, having said that, some of the better intercoms/audio panels employ sophisticated signal processing techniques to help clean up the audio coming from the mikes. Do they send the "cleaned up" signal to the radios? I would presume so, but really don't know.