Mobile Design

Mobile First is a concept developed by Luke Wroblewski and highlights the belief that web pages shoul be designed for a mobile interface first, and then expanded to work on all screen sizes.  

The links below use a combination of flexible grid design, and fluid grid design.  They also talk about using css media queries to identify styles for multiple screen sizes.
http://www.lukew.com/ff/entry.asp?933
http://www.lukew.com/presos/preso.asp?26
http://labs.thesedays.com/blog/2010/07/16/10-tips-for-designing-mobile-websites/
http://css-tricks.com/resolution-specific-stylesheets/