via IBM developerWorks: Create Ajax applications for the mobile Web.
Good tutorial. It starts out with a trivial Java app to create content, but any other server side tech, like PHP, could be used. The mobile portion relies on HTML 5 and AJAX in iPhone OS 3.x+ and Android 2.x+ browsers. You’ll need the most recent Adroid and iPhone SDKs to put this together.
This article provides a good starting point to start looking at how to build basic mobile apps.