I need to create a contacts application that mimics the native android contacts application. The applications needs to be ported on all the android devices and should support the fields that a native application contains.
I need to know what all fields does the Content provider supports and how does it deal with the devices in which the stock contacts application is modified (e.g HTC Hero )
The Android SDK has pretty detailed information about the contacts provider - everything that is supported is detailed there. I assume that your application will be 2.0 only - if you want to support older Android phones as well, you'll basically have to do the same work twice and use the old contacts API. Again, whatever the (old) documentation says is supported there.
Since the content provider is in the ROM, modified apps don't use the contacts provider - they have their own content providers on top of the existing ones to handle all additional fields. The Hero for example has its own content provider with the "events" for contacts, and those are proprietary - your best bet is to get a rooted phone and dump their SQL databases with adb.