Following on from the public release of iOS 7, a number of users have reported issues with the iMessage service, reporting an inability to send or receive messages in a timely manner. Apple has now made a statement to the WSJ saying that they are aware of the the issues and that they only affect a fraction of a percent of iMessage users. As such, the company is working on a fix that will be released as part of a future iOS software update, although it is not clear if the fix will be included in iOS 7.0.3.
Anecdotal reports around the web have provided potential interim fixes for the problems, but the effectiveness of these fixes is not fully established. Some users have reported that turning off iMessage on their iOS device, followed by a reset of networking settings and re-enabling iMessage has solved the issue. Others have reported that they are still having problems after attempting this fix (which notably will erase all saved Wi-Fi passwords on an iOS device).
With Apple aware of the issue, a fix will hopefully come in the next few weeks rather than months down the line.