I had never thought about this until I read this article on MSNBC: Stevie Wonder: Touch-screens alienate blind.

The problem, of course, aren't the touch screens per se, but the fact that usually touch screen application don't allow for any other input mechanism -- think of the iPhone.

Here's another review...

Using camera-phones to interact with context-aware mobile services

In this technical report [Toye et al., 2004], the authors present the results from a study on a new interaction technique that uses camera-phones and visual tags to interact with public displays.

The technique consists in using visual codes in printed form or in dynamic displays that a camera-phone can recognize. The mobile phone communicates with a computer so that when a user 'clicks' on a tag, the display can reflect that action as if a button was pressed, for example. Also, the mobile can be used as a secondary display and also store information and personal data that is sent automatically to create a personal interface.

Here's my review. Comments are appreciated... 

The Design Space of Ubiquitous Mobile Input

[Ballagas et al., 2008] presents a design space of mobile input techniques with five dimensions: graphical subtask (position, orient and select), dimensionality, relative vs absolute movement, interaction style (direct vs indirect) and feedback (continuous vs discrete).