Manufacturers bury their warnings deep within their manuals:
“Keep iPhone at least 15 mm (5/8th inch) away from the body.”
On your iPhone: Go to Settings > General > About > Legal > RF Exposure
“For body-worn operation, this phone has been tested and meets FCC RF exposure guidelines when used with an accessory that contains no metal and that positions the mobile device a minimum of 1.5cm from the body.”
Galaxy II – User Manual – Page 164
“Keep the BlackBerry device at least 0.98 in. (25 mm) from your body (including the abdomen of pregnant women and the lower abdomen of teenagers)”.