There are members of Apple's Support Communities complaining that since the update to iOS 7, they have been having problems with iMessage; some of the complaints include messages that are not being sent, and messages not being received. The problem doesn't appear to be with Apple;s servers because the messages are supposed to be sent as SMS texts in that scenario, which is not the case...Source: http://www.phonearena.com/news/Some-Apple-iPhone-owners-complaining-of-problems-with-iMessage-since-iOS-7-update_id47860
