Will it be upper-case or will it be lower-case: can a prompt for text be a mode signal?

The new forms of interaction being devised for small mobile devices have required designers to re-visit basic principles for user interface design. One of these is the notion of mode. For example, when a key is pressed how will the user know whether the letter displayed will be in upper- or lower-case. An experiment is described in which users have to learn to use a new device where this is an issue. Results show that users are influenced by the case of letters in the prompt.