If you are using phonegap/cordova versions 1.5+ you can create a native tabbar with this plugin: https://github.com/AndiDog/phonegap-ios-tabbar-plugin
Other phonegap/cordova plugins can be found here: https://github.com/phonegap/phonegap-plugins/tree/master/iOS
Here's a tutorial how to implement this: http://zsprawl.com/iOS/2012/03/using-the-native-tabbar-plugin-in-cordova/
This is of course the best approach. Other one would be to use a jQuery Mobile and create a HTML tabbar. This is a harder way because it will take time to style it properly and even then it would not fully act as a native tabbar.