iOS display notification based on incoming phone call

Is it possible to have a background app display a notification based on who is contact details from 开发者_运维百科an incoming caller, either before the call is answered or during?

No, the system will not allow you to interact with phone calls in any way.

You can set the image for certain people in the address book using the Address Book API. That way, a certain background image (potentially with a textual message) will be shown, based on who is calling.

With time, things change. Look at sync.me, when you get an incoming call, the latest post on facebook will show just above the accept/decline button. Though I still can't get the idea of how it is done.