I just got the same email. I got on here to post a new thread (but of course this thread was already here). I have two iPhones on the way, one for my wife and one for me. They were ordered separately, mine shipped 24 hours after hers and her tracking shows hers as farther along than mine. Even so, the FedEx tracking for mine still shows a delivery date of June 23, while hers shows the 24th. The email didn't have an order number or any other way to tell which order its referring to. I wonder if that means they'll both show up on Wednesday. Here's hoping...
Edit: To clarify, the original Apple shipment notification emails for both phones showed a June 23 delivers by date. For my wife's phone, the actual FedEx tracking has always shown the 24th, while my phone has always shown the 23rd.