(FORTUNE Magazine) – At every break during Nokia's analyst meeting last year in New York City, hordes of analysts and pundits rushed out to make calls. Nothing unusual about that. But more than half of the callers were using a headset wire with their cellphone. When the wireless experts make calls, they play it safe.

For more than a decade I've written about the potential health effects of electromagnetic fields from cellphones and other devices. The conclusion? Not enough is known to say whether cellphones are safe. And while publicity about the issue waxes and wanes, lately it has reemerged with several breakthrough studies and a major lawsuit.

--The most potentially incendiary research was published in August in the European Journal of Cancer Prevention. A team led by Swedish oncologist and epidemiologist Lennart Hardell demonstrated that users of analog (nondigital) cellphones were significantly more likely to develop a brain tumor than nonusers: The longer they used the phones, the greater the risk of cancer. The study also found that people who had brain tumors were more likely to have them on the side of the head where they held their analog phones (results for digital and cordless phones were inconclusive).

--Separately, scientist Dariusz Leszczynski recently published a Finnish laboratory study that found that one hour of cellphone-type radiation affected the production of proteins in cells. Though there is no evidence that this is a health risk, Leszczynski says he worries that such changes in the brain--right next to the phone--might increase the permeability of the blood-brain barrier, which could be dangerous. Any evidence of biological effects from cellphone radiation--and there has been a steady trickle of it for years--is potentially worrisome.

The U.S. cellphone industry basically dismisses all the studies and shows little enthusiasm for additional research. While official government bodies or advisory groups in France, Germany, and Britain recommend reducing exposure to phone radiation, especially for children, U.S. regulators are silent on the matter.

The cellphone industry is clearly terrified of liability. A federal judge in Baltimore is about to decide whether to let the case of a brain-cancer-stricken neurologist, Christopher Newman, who has sued a variety of cellphone players, go to a jury trial. Newman is represented by the firm of Peter Angelos, which has reaped huge fees from actions against asbestos and cigarette manufacturers. If this goes to trial, expect major headlines this fall on cellphone safety.

About one billion people worldwide now use cellphones, and the number is growing rapidly, leading some scientists to call the use of cellphones the biggest biological experiment in history. Says Louis Slesin, editor of Microwave News, the most comprehensive source of information on electromagnetic fields and health: "Anybody who tells you that cellphones are either safe or unsafe doesn't know what they're talking about. It remains an open question." Slesin urges much more aggressive research. In the meantime, those little headsets are inconvenient but reassuring.