Mobile web app development

Check out : http://www.slashdotdash.net/articles/2007/12/04/iphone-on-rails-creating-an-iphone-optimised-version-of-your-rails-site-using-iui-and-rails-2

It is upto you whether you want stripped down html or WAP.

Cameron Moll has a mobile web ebook that I've heard good things about:
http://mobilewebbook.com/

Michael Slater
www.BuildingWebApps.com
www.LearningRails.com