A piece of code need to be executed even after the iPhone app sent to background. Based on the values the UI need to get changed. When I bring the App to foreground.It need to be updated with the changes made at the background time.
Eg.When I sent a GPS application to BackGround.It need to receive the positions accordingly and update the UI.
As far as i know, you may not update the UI while in background (As per memory guidelines, you should release any unused/cached portions of your interface). However, you can schedule your update to the moments after your app is reactivated.