Users are complaining that messages appear to be sent but are later updated with an exclamation mark indicating that they were not. Some users are able to resolve the issue by restarting their device or resetting network settings from Settings:General:Reset:Reset Network Settings.
“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,” says Apple. “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.”
Notably, it was reported today that Apple has already seeded iOS 7.0.3 to employees and partners for testing.