For people addicted to typing messages on their handheld computers, the American Physical 
Therapy Association has released a series of hand exercises that can reduce the chances of developing "Blackberry thumb."
The repetitive strain injury is caused by overuse of the thumbs to type messages on the popular Blackberry e-mail device from Research In Motion, or any other handheld computer with a similar keyboard. "The thumb isn’t a dexterous digit, so it’s not use to working in this manner," Margot Miller, president of the Occupational Health Group for the APTA, said Monday.
Ignoring the discomfort from strained thumbs can lead to swelling and throbbing at the base joint, and, in extreme cases, Cortisone injections and surgery, Miller said. How To Avoid ‘Blackberry Thumb’ - News by InformationWeek