You want an Offline Web Application.
This article seems to explains step by step how to do this.
http://diveintohtml5.info/offline.html
Creating a website like this, will allow you to bookmark it and have a shortcut icon in the phone's dashboard that will allow you to load your page in the browser for those cases where you don't have a data connection. In the case where the phone has a data connection, it will load the manifest to check if there are any new files to update the application. I don't think there is a way to make it truly offline though.