The recently announced...

Google Custom Search for mobile

...lets web site owners add a Google Custom Search box to site pages that provides optimzied mobile display friendly results for phone Android, iPhone (iPod touch) and Palm Pre phones.

Specific information on implementing this for your website is found in the Google Custom Search Blog entry...

Google Custom Search for your smartphone

The trick is to either redirect people visiting your mobile web page to a Custom Search page or simply providing a link with your personal Custom Search ID.

I haven't gotten around to trying this with my personal sites. But, it is in my to-do queue.