Doctors have recently started diagnosing a new type of ailment that could be attributed to the devices that have a tiny keyboards for typing messages. They are calling the new joint soreness, "Blackberry thumb" after the famous handheld email device the Blackberry. This article in the washingtonpost.com explains the ailment in more detail. It sounds like it is caused by extensive use of your thumbs typing messages which is similar to the carpal tunnel syndrome you can acquire from typing on a computer keyboard.
For some reason, "Blackberry thumb" reminds me of the 1979 film The Jerk starring Steve Martin where Steve's character, Narvin R. Johnson, invents a new device to grip eyeglasses and becomes very rich only to find his fortunes swept away from him due to lawsuits filed when the eyeglass gripper caused its users to slowly go cross-eyed. I wonder what handheld device makers are thinking about "Blackberry thumb"?
