Apple has today acknowledged that there is in-fact a problem with iOS 7 and iMessage, and that it has affected “a fraction of a percent” of its users. Some users are not able to send iMessages as delivery of the messages are failing. Apple says a fix is coming soon.
We are aware of an issue that affects a fraction of a percent of our iMessage users, and we will have a fix available in an upcoming software update,” Apple said in a statement. “In the meantime, we encourage any users having problems to reference our troubleshooting documents or contact AppleCare to help resolve their issue. We apologize for any inconvenience this causes impacted users.