To users and developers there is no difference between an application that has been rejected and one that has not been approved, either way the app still isn’t available. But, to Apple, there is a difference.
Imagine a file named “todo.txt” sitting on your desktop. Inside the file is a list of things that you want to get done. Deleting that file means that you aren’t going to accomplish the items on the list. We all know how people are with to do lists, they get put off and often times never get done. But, rather than admit that you’re (most likely) never going to get the items done, you leave todo.txt on your desktop and, if asked about it, you would say that you are “working on it.” You still haven’t done any of the items on the list but you also haven’t decided that you aren’t going to do them.
Google Voice is todo.txt and right now it is sitting on Apple’s desktop. They haven’t placed it in the Trash yet (rejected it). But, they likely aren’t actively doing anything with it either. Apple is “working on it” just like you are.
Update 10/4/09: Apple and Google Slowly Parting Ways