First, thanks a lot unity team for this awesome update!
Full support for native Objective C and C++ code opens full access to the iPhone 3.x APIs and custom plugins.
Can anyone tell me what does this really mean and do?
Does this mean that I can access to new iPhone features like compass and ad-hoc play?
It means you can access any Object C function right from scripting after you have created a corresponding “DLLImport” declaration from it and a C handling function to interface with Unity
That can be anything you have written in ObjC, you just need to know how to handle it through the System.Runtime.InteropService and the related classes in that namespace.
Also, you need Unity iPhone Advanced to use that
You need to write functions in C that access the Cocoa features you want, and then you declare them in your Unity code via DllImport statements. Check out the docs and the sample code.