GSM noise is a bug, but in the devices it shows up in, not the phones
Any conductor is an antenna for electromagnetic radiation, of any frequency, they just work on some frequencies better than others. This means that circuit traces on circuit boards and wires inside electrical devices are antennas, and they will pick up radio signals, across the spectrum. Some of the radio signals have data rates that are too fast for the human ear to hear, though, so we don't notice them. The GSM network apparently has some data rates in the audible range, so we notice the noise.
There is in fact a bug if you're hearing the noise, but it's in the equipment in which you hear the noise, not the equipment producing the noise. Manufacturers of audio electronics should be aware of these facts, and they must include a "Farraday Cage" around their circuits. Items like the Belkin iTrip, my Volvo's sound system head unit, and 3rd party stand up speakers are just three examples of poorly designed audio electronics that do not have a Farraday Cage, because, well, they tend to be heavy, and industrial designers don't know much about electrical engineering.
A Farraday Cage is an electrically conducting "cage" with holes no larger than half the minimum wavelength you wish to block. A MacBook Pro is a good example of electroincs with a Farraday cage, as are most computers - since they have a metal enclosure. Airplanes are another example of a Farraday cage, though the windows tend to let through most higher frequency signals.
I could tell you stories of building Farraday cages when I worked in a physics lab to prevent radio signals from interferring with power controlling integrated circuits, but I'll just put it in this off-hand comment instead.
It's sad that in this day of the proliferation of radio and audio devices that the industrial designers of so many products have absolutely no idea how to make them compatible. Again, there is a bug, but it's in the hardware design of the devices in which you hear the noise, not the phone.
(Another off hand comment, you can solve this problem in some cases by wrapping aluminum foil completely around the devices that need protection, but since it's so thin, it genenrally also needs to be connected to electrical ground. This is similar to the way the earbuds are protected, by a grounded, conducting shield around the signal wires. You can buy special shielded cables from audio professionals, but they tend to be much more expensive. Plain "speaker wire" at Radio Shack is a great example of unshielded cable that will let in noise if the signal is powerful enough.)
(Farraday cages work by becoming antennas themselves. They intercept the radio signals before the signals can get inside.)
