Mobile Development in Windows SharePoint Services
This is a good overview and starting point for customizing SharePoint for consumption by mobile devices. From the page:
"This section provides information about the kinds of customization that you can make to the pages used for access to Windows SharePoint Services data through mobile devices.
You can take two basic approaches to customizing mobile pages in Windows SharePoint Services:
Create custom mobile pages from scratch and let Windows SharePoint Services redirect users to these pages.
Override an existing Windows SharePoint Services mobile control template to create a unique mobile Home page by site definition type, or a unique mobile view page according to site definition type and list definition type.
Use the first approach to create an additional custom mobile page from scratch and use it as a Windows SharePoint Services mobile page. Use the latter approach to customize some part of existing Windows SharePoint Services mobile pages through user controls (.ascx files)."