I am on an iPhone 4S. My husband is on my old iPhone 4 w/ iOS 5. iMessage works flawlessly for him. Me, not so much. Every time I send him a message, I get a delivery failure. If it tell it to try again, it will go through as an iMessage on the second try. SMS works fine. Any ideas what could be causing this and how to fix it? It's completely annoying. Thanks.