WARNING: Holding a cellphone against your ear may be hazardous to your health. So may stuffing it in a pocket against your body.

I’m paraphrasing here. But the legal departments of cellphone manufacturers slip a warning about holding the phone against your head or body into the fine print of the little slip that you toss aside when unpacking your phone. Apple, for example, doesn’t want iPhones to come closer than 5/8 of an inch; Research In Motion, BlackBerry’s manufacturer, is still more cautious: keep a distance of about an inch.

The warnings may be missed by an awful lot of customers. The United States has 292 million wireless numbers in use, approaching one for every adult and child, according to C.T.I.A.-The Wireless Association, the cellphone industry’s primary trade group. It says that as of June, about a quarter of domestic households were wireless-only.

If health issues arise from ordinary use of this hardware, it would affect not just many customers but also a huge industry. Our voice calls - we chat on our cellphones 2.26 trillion minutes annually, according to the C.T.I.A. - generate $109 billion for the wireless carriers.

The cellphone instructions-cum-warnings were brought to my attention by Devra Davis, an epidemiologist […]