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A spokeswoman for Apple, Natalie Harrison, provided a statement in response to questions about the iPhone warning. "iPhone's radio-frequency energy is well within the limits set by the Federal Communications Commission of the U.S., Industry Canada of Canada and other countries," she said. Representatives for Motorola and Research in Motion did not respond to requests for comment.
John Walls, a spokesman for CTIA, a trade group representing the wireless industry, confirmed that the warnings arose from the FCC testing guidance. "Because they test at the waist in the holster, any reference to use guidelines or advice incorporates the buffer the holster provides," Wall wrote in an e-mail to TIME.
So should you be worried about putting your phone in your pocket? The answer depends largely on how much faith you put in the current state of scientific research about radio-frequency energy.
Both U.S. and international regulatory bodies like the World Health Organization have found that available scientific evidence does not demonstrate an increased health risk due to the radiation that is emitted by cellular phones. But these statements, which are based on large studies looking for increases in conditions like brain cancer, do not rule out the possibility that future studies might reach a different conclusion, as more data is collected over longer periods of time and the general use of cellular phones increases.
The FCC notes on its websites that studies linking radio-frequency exposure and cancer "have been inconclusive." The Food and Drug Administration (FDA), which has primary responsibility for monitoring the health science of cellular phones, has stated that it cannot rule out the possibility of a health risk from phones, but if such a risk exists, "it is probably small." One recent study found that people who used their phones most often and for the longest period of time 30 minutes a day or more on average for at least 10 years had a substantially higher risk of developing some form of brain cancer, but the study also found that those who rarely used cellular phones had a lower risk than those who used only corded phones.
The FDA recommends that those concerned about these health risks can either reduce the amount of time spent using a cell phone or "use speaker mode or a headset to place more distance between your head and the cell phone." If using a hands-free headset, the FDA recommends keeping a distance between your phone and your body, either by holding the phone in your hand, where it is likely to be less of a hazard, or in an approved body-worn accessory like a holster.
Given the current testing guidelines, it is impossible to know if any phone currently sold in the U.S. would exceed 1.6 watts per kilogram if worn in a pocket flush with the skin, or by how much. But the fine-print warnings suggest manufacturers are aware of the possibility. The BlackBerry 9000 warning, for instance, states that users should "use only accessories equipped with an integrated belt clip that are supplied or approved by Research In Motion" to "maintain compliance" with FCC guidelines.
In a recent update to its online advisory on cell-phone radiation, the FCC noted, "Many people mistakenly assume that using a cell phone with a lower reported SAR value necessarily decreases a user's exposure to RF emissions, or is somehow 'safer' than using a cell phone with a high SAR value."
The posting went on to explain that any given phone could have several different emissions levels in various configurations, and that FCC testing is only designed to ensure that the phone does not exceed 1.6 watts per kilogram of exposure in a "most severe, worst case (and highest power) operating conditions." The Web posting, however, did not explain why FCC testing fails to account for the worst-case (and quite common) scenario of a cell-phone user who wears a phone against the skin inside a pocket.