UIWebView Expose Objective C to JavaScript
The best way to do this would be through a custom link, and then use the UIWebView delegate method -webView:shouldStartLoadWithRequest:navigationType: to trap requests. When you see a request come through with your link in it, you know your action has been triggered.
There is an example application in the QuickConnectiPhone framework that shows you how to do this.
QuickConnectiPhone also gives you a JavaScript function called 'makeCall'. You pass it a command and an array of parameters and it will pass them to the Objective-C side of your app for handling. You can then make your function call.
You can find it here on Sourceforge.
To see an example of this check out the PhoneGap source code from Github:
http://github.com/sintaxi/phonegap/tree/master/iphone/Classes/GlassAppDelegate.m