From the Trend Micro website:

"Trend Micro™ Mobile Security is designed to protect data-centric mobile devices such as smartphones against viruses and short message service (SMS) spam."

Available for free but the product will expire on June 30, 2005 September 30, 2005 30 days after installation. Who would ever have thought a few years ago that he would have installed an antivirus software on his phone??

More information
Direct to download

BTW: In a previous post on my blog you'll find links to several antivirus products that you can use on your home desktop PC for personal use only.

Update (July 3, 2005): Trend Micro now has a new version for download that will expire on September 30.
Update (March 27, 2006): The free version has been replaced by a 30 day trial version.