From what I've heard, OS 4.5 is back to beta again. There have been many bugs to work out and I doubt if we'll see any releases in April at all. There are still bugs in the .21 version that is rumored to be in testing now. Even after a good (relatively) bug free version hits the carriers they will have to test some more to make sure no other bugs have been introduced. It's going to be a while, folks.