i\'m trying to create an app which uses the combination of native functionality and the phoneGap framework. The native app has a button, upon the click of which the phoneGap ui
Yes, this is possible. Although you might be getting yourself into some headaches. My app kind of goes the other way around, it's mostly phonegap, but occasionally i'll pop open a view that is native. Here is the link to code that shows an excellent example of how to switch between the iOS and phonegap worlds.
new updated recommended article (see update below)
These files represent a standard plugin used in phonegap. In this particular plugin, a native view is opened on top of a phonegap view. Notice you have a custom xib and everything. This plugin can be modified to display any xib with any functionality you could think of.
If you implement this plugin you will easily see how to jump back and forth. I've successfully heavily modified these classes to add LOTS of native capabilities to my phonegap project. Also you should probably check out the official phonegap guide to phonegap plugins. Here
Important Edit
Was informed original linkwas broken (not terribly surprised as this answer is very old and i've long since moved away from Phonegap) so I replaced the original link with an article that shows how to do these plugins well. In the article it explains the link is broken and gives several links where these older files are maintained, but in fact those are broken as well. Here is a branch of one of them I found that still hosts the original files on an "archive" branch. But I haven't investigated whether these files are wildly different from my original work. Good luck!