BlueTooth emits less EMR than an actual handset, so it does help reduce overall exposure (assuming you're talking about a BT earpiece - a handsfree speaker/mic would reduce it to negligible at most). A standard wired headset is the "safest" bet (although there's a pretty silly academic debate about whether or not they still produce enough EMR to affect a user over the long-term - measurements are so low as to be difficult to even gauge).
With regards to the study and the history of this debate, there seems to be an element of common sense involved - a (albeit weak) microwave transmitter held against one's head for extended periods is probably not the wisest behavior. The evidence does show any damage is likely cumulative, so for those of us who don't have frequent, really long cell phone conversations, it's probably not an issue. For people like my brother who tends to spend many hours a day on a cell (and has since they were "bag phones"), it should be of some concern. Our bodies simply aren't equipped to absorb long term EMR. Just like they aren't designed to breathe smoke and process large amounts of alcohol - back to the good 'ol "all things in moderation" rule :wink:
The report said "possible" not cancer causing. It also presented no real data with any meaning. The actual numbers don't stand up. They claim a 40% increase of a certain kind of cancer, but also stop short of causation. It just doesn't make sense. With billions of people now using cell phones, other reseachers report that there hasn't been any noticeable spike in cancers. So where is the WHO getting their data?
I call BS. Of course, I don't use my phone for 30 minutes a day anyway and I use a wired headset most of the time.