Check out PhoneGap – a dev tool which lets you code up standard apps in HTML, CSS, JS / JQuery, etc, and then compile the whole lot as a mobile app.
Behind-the-scenes it uses the phone’s browser to render the HTML code.
Downsides to it are that each platform (iPhone / iPad / Android / Blackberry / etc) need their own CSS / etc in order to look like native apps
JQuery Mobile is something also to look at.