An Argentine study mentioned in the July/August 2011 issue of Men's Health Magazine, p.33, explains that cell phones worn on the belt may be related to lower bone mass. "Men who regularly carried a cellphone on their right hip had lower bone mass at the top of their right femur than men who didn't carry a phone."
The study comes on the heels of a recently released report by a team of international scientists claiming a possible link between cell phone usage and cancer. Read my article published on Yahoo! and Yahoo!News, "World Health Organization unlikely to get people off the phone" for more information about the WHO classification of cell phones as potentially "carcinogenics to humans."
It's worth noting that both studies speculate that radiofrequency radiation might possibly affect cell formation and alter the natural coarse of things and lead to health-related issues.