Few days ago, the jQuery team announced that they are working on jQuery Mobile which will probably become quickly popular on creating mobile web apps. for the fans of the library.
On the other hand, there are already ready-to-use solutions like the pretty-complete jQuery iPhone UI (check the “Mobile Development” category for others).
It is a jQuery library which emulates the iPhone interface that is handy for creating iPhone web applications.
The library includes widgets like menu, tabs, scrolling, forms and gallery browsing.
jQuery iPhone UI is not complicated to use and comes with a documentation to get you started.
Website: http://iphone.hohli.com/
Download: http://code.google.com/p/jquery-iphone-ui/do