Like many users, San Francisco entrepreneur Zaidman likes the convenience his cellular phone affords -- the ability to chat with business associates or friends in the car or while walking down the street.
But he worries about the invisible waves of radiation emanating from the phone.
"I have an intuition that they're not safe," said Zaidman, who says he gets headaches after using the phone near his head. "I try to keep it away from my head as much as possible. When I get a call and I can't find my headset, or I'm not in my car (where he can put it in a cradle in the dashboard), I tell them to call me back."
Zaidman isn't alone in his ambivalence.
While the number of cell phone users continues to balloon -- about 1 billion people worldwide will own cell phones by 2003, according to the research firm Gartner Group -- recent studies and several foreign governments' recommendations about curbing children's use continue to stoke concerns about potential health effects.
To be sure, the research so far is not conclusive, and the picture won't become clearer until long-term studies emerge in the future.
Still, the nearly decade-old doubts about the device's safety won't fade away, despite a growing amount of evidence that people are worrying needlessly.
Earlier this year, a study that tracked the health of 42,000 cell phone users in Denmark found no link between the devices and certain cancers, including brain and nervous system cancers. That study echoed the findings of two smaller U.S. studies, leading many to conclude the gadgets are safe.
What's more, the cell phone industry is quick to point out, the devices have saved innumerable lives and prevented injuries during emergencies. In addition, the Federal Communications Commission says most cell phones pose no threat. The agency limits radiation emissions from cell phones and says its guidelines include a large cushion between allowed levels of exposure and thresholds known to harm health.
"The science to date shows that there are no adverse health effects (of cell phones), and the FCC agrees with that position," said Travis Larson, spokesman for the Cellular Telecommunications and Internet Association (CTIA), a wireless trade group in Washington, D.C.
Nevertheless, some scientists and consumers say there's not enough research, and what research is being done may be too narrow.
Some say the industry, which teamed up last year with the Food and Drug Administration on future cell phone-health research, doesn't want to pop the $108 billion cell phone bubble.
According to Gartner, nearly 419 million phones were sold worldwide in 2000.
And despite the recent high-tech downturn, Gartner still estimates about 683 million phones -- worth about $30 billion in revenue -- will be shipped in 2003.
Other critics say the studies to date, namely the large project in Denmark, yielded only a sliver of relevant data. That's because while several thousand of the subjects used their phones for more than 10 years, most had used the phones only for about three years.
It's irresponsible for the industry to tout the Danish study as the definitive work on this matter, said Henry Lai, a professor of bioengineering at the University of Washington.
Lai released a study in December that found that rats exposed to cell-phone- like radiation suffered breaks in their cells' DNA -- the microscopic strands that carry an organism's genetic code.
Lai and others say the FDA and CTIA research is focused too narrowly. A study about to begin will examine a form of cell damage called micronuclei; two studies on the subject had divergent results. The two groups are also examining future topics of research.
Meanwhile, the British and French governments have released recommendations advising parents to limit childrens' cell phone use. Though the recommendations didn't point to a specific link between cell phones and adverse health effects, several overseas labs have indicated a range of possible health effects from cell phone use -- including cancer, sleeplessness, blood disorders, headaches and changes in cognitive functions.
"Is the whole world crazy and we're right? I don't think so," said Louis Slesin, editor of New York's Microwave News, a newsletter about electromagnetic radiation and health. "People are generally in love with their phones, maybe even addicted. (Cell phones) are not going away. But the question is, can you design a safer phone? And the answer is, yes, you can."
Slesin says Congress should move quickly and order the FDA to study -- and settle -- the issue now.
The industry "takes all research seriously," said Peter Harrison, Nokia's director of electromagnetic field issues. "And yes, there have been some findings. But none of those findings have been replicated or confirmed in any way."
It will probably be years before the earliest cell phone users are old enough to provide a clear picture of any long-term effects of cell phone use on humans.
Until then, Zaidman is keeping his cell phone antenna pointing at the sky rather than his cranium.
"In the long run I think it's probably not a safe thing," he said. "I know the industry says there's no evidence to date to suggest cell phones cause cancer. To me, that sounds like the claims made just as loudly and clearly about smoking 30 years ago."