Ever since I installed ios 7 on my Verizon iphone 5, when an iMessage doesn't go through, it just keeps trying to send as an iMessage instead of converting to a text message after a minute or two. I have to go back to all my messages and make sure they've been sent, or long press on which ever one hasn't been sent, and select the "send as text" option. And yes, I have the option checked already for iMessages to deliver as text messages as needed in settings.