Safety Information

As part of a new project, I get to play with a couple of cell-phones. While reading through the manual of one of these, my eye caught the following piece under the section for "Safety Information":

Repetitive Motion
When you repetitively perform actions such as pressing keys or entering finger-written characters, you may experience occasional discomfort in you hands, arms, shoulders, neck, or other parts of your body. If you continue to have discomfort during or after such use, stop use and see physician.

Now I'm wondering, just exactly which 'other parts of bodies' have been used to REPETITIVELY press the buttons on the keypad of a cellphone. Enough so that the manufacturers felt it necessary to include this clause in their warning.