You’ll need the ChildBrowser plugin with PhoneGap in order to return to the app after clicking on an external link. A Done button will appear under the web page, allowing you to exit the web page and return to the app. Very convenient. I’ve had to search and experiment for two weeks before I could piece all the correct steps together. If you landed here early, you can do it all within an hour!
UPDATE 6/5/2012: For PhoneGap-Cordova 1.7.0, use these steps to install ChildBrowser:
UPDATE 3/21/2012: For PhoneGap-Cordova 1.5, use these steps to install ChildBrowser: http://blog.digitalbackcountry.com/2012/03/installing-the-childbrowser-plugin-for-ios-with-phonegapcordova-1-5/