Efficiently converting a web UI to be better viewed on an iPhone or Android device?

Problem

I'm sure there are plenty of discussions about this floating around, but I'm curious what may be considered most useful by folks in the community here presently:

What is a solid approach, css framework or otherwise that would facilitate proper display of a web app on an iOS device (meaning, in particular, iPhone displays) or Android devices?

This is especially pointed at a web app that's already done UI wise and so I'm looking to tune the display a bit, although it already looks good, it could be a little more clear for smaller displays.

Problem courtesy of: ylluminate

Solution

Have a look at jQuery mobile and also Sencha framework.

Solution courtesy of: ASH

Discussion

Is there any need to use Jquery mobile or sencha. Cant he display the web UI on iphone or android browsers using any User Agent.

Discussion courtesy of: math

I have rather mixed feelings about jQuery mobile, but it does give you an almost-native-app look & feel out of the box.

Discussion courtesy of: josh3736

This recipe can be found in it's original form on Stack Over Flow.