Ok, as an amateur (ham) radio operator, this is just screaming for me to make a response! Think about this logically:

1. If you "shield" your transmitter (cell phone, wi-fi device, cordless phone, Bluetooth headset, whatever) so that the signals don't go out, how will it communicate with the other end? If your body is between you and the transmitter and you shield it, you'll lose the signal, right? (Technically, your body IS a weak shield at these frequencies--otherwise your microwave oven wouldn't work. Ditto for clouds killing the signals to your tiny satellite dish, and for the same reason: water. YOU are a bag of mostly water!)

2. I don't know about elsewhere, but here in the USA the FCC (our telecom regulatory agency) uses Specific Absorption Rate (SAR) calculations--for more info, see the Wikipedia entry at:

http://en.wikipedia.org/wiki/Specific_absorption_rate

Note how it is measured in Watts per Kilogram; like talking about the difference between the joule (a unit of energy) and the watt (energy usage of joules per second), understanding SAR means resizing actual measured energy (very low) into larger units (W/kg). Remember that all cell phones have an upper transmitter limit of 600mW (0.6 watts), which isn't much; wireless ethernet generally is less than that, though some access points get close; and Bluetooth and some other unlicensed devices are even less than that, such as the FM radio transmitter in the N900 who's output is, from what I read, 10 or 50 nW (nanowatts, millionths of a milliwatt or billionths of a full watt).

Ok, so what does this mean in the real world? It means that if actual damage comes from tissue heating, you'd need to heat it for a long period of time (talking with the phone next to your ear for an hour or more MAYBE) or have a small amount of power directed to a small spot using a directional antenna rather than the more-or-less omnidirectional one you have in your phone: this is why standing in front of microwave dishes with transmitters such as VSAT terminals is a very bad idea, especially if they're transmitting continuously. OTOH, a sector on a typical tri-sector cell site has a 120 degree angle (equilateral triangle) or even 90 degrees on some sites and are used to limit the size of the resulting cell rather than attempting to get major antenna gain, so even when fed with 50 watts (of which maybe 40 actually makes it to the feed point at PCS frequencies I'm guessing, maybe even less when the diplexers and filters are taken into account), unless you're standing in front of them, I doubt you're in any danger whatsoever from radiation alone, although you'd need a field strength meter to make absolutely sure.

One last thing: there has been some talk for years now about TDMA modulations--this includes GSM, the old TDMA system (IS-56 and IS-136 if I remember right), Motorola's iDEN (Nextel, Mike, etc), and perhaps some other trunked radio systems. Basically, if it makes a "buzz" in your stereo system when you make a call, it's TDMA (Time Division Multiple Access) and the problem is that very "buzz" possibly messing with your nervous system in the same fashion. The buzz comes from the transmitter turning itself on and off at a certain frequency: you'd see it as a low frequency square wave on an oscilloscope. The trouble is that the frequency of this buzz is similar to that in animal nervous systems, including the human brain, and there is though that THIS could be the real reason for the trouble with phones. Unfortunately, the only way to know for sure is to make side-by-side studies of people who use those technologies with those who use other, more "continuous" technologies (AMPS and CDMA), but no one has done this; compounding the problem is that AMPS has virtually disappeared worldwide AFAIK, CDMA is only used widely here in North America, and both GSM and CDMA are often found at the same shared cell sites.

I hope all this helps.

Mike

UMTS usually uses W-CDMA, so definitely not only used in the US.