WARNING: Holding a cellphone against your ear may be hazardous to your health. So may stuffing it in a pocket against your body. 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. 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. Devra Davis, an epidemiologist who has worked for the University of Pittsburgh ... has published a book about cellphone radiation, Disconnect: The Truth About Cell Phone Radiation, What the Industry Has Done to Hide It, and How to Protect Your Family. Her book ... surveys the scientific investigations and concludes that brain cancer is a concern. Children are more vulnerable to radiation than adults, Ms. Davis and other scientists point out. No field studies have been completed to date on cellphone radiation and children, she says. 28 percent of studies with cellphone industry funding showed some sort of effect, while 67 percent of studies without such funding did so. Ms. Davis recommends keeping a phone out of close proximity to the head or body, by using wired headsets or the phone's speaker. Children should text rather than call, she said, and pregnant women should keep phones away from the abdomen. The best way to avoid exposure [is] by holding the cellphone away from the head or body.