So, looking for a needle in a haystack, and hoping there's an audio-engineer or RF engineer out there that has enough experience in this that can help (I've done some googling, but to no avail as of yet). I love my iPhone, but its GSM radio interference with audio devices irritates the hell out of me as a music and audio lover (avoiding saying "audiophile" here...). The interference is caused by power bursts that are at an approximate 200 Hz interval (one reference). I notice that when I put my hand around the antennae, most of the interference goes away, yet I only loose about 1 bar (granted, I'm in northern VA, so strong signal to begin with). I figure with 200 Hz in the audio spectrum, you should be able to use regular sound-proofing materials to weed out the 200 Hz interference from the iPhone. Of course, we'd want a material that is transparent to higher frequencies (the proper GSM frequencies). With that... anyone have any ideas? Foam is probably not a good solution, as I'd want this to be somewhat compact. How about different (specific) rubbers? What are the absorption qualities of them?