It appears that Apple's iMessage service is down for users of the iPhone, iPad, and iPod touch. Users in North America and Europe are reporting that they are unable to send iMessages out from their devices.
Oddly enough, the service still seems to be working on OS X when sending messages to email addresses, but not to phone numbers. with messages sent from Mac computers even syncing back to iOS devices. But when a user tries to send a message out from their iOS device, the system hangs and the message fails or reverts to an SMS if possible.
We have been unable to send messages with any of our iOS devices in New York, Boston, San Francisco, or London, but the problem may be even more widespread than that. A quick search for "iMessage not working" on Twitter shows that many users are apparently experiencing the problem. We have reached out to Apple for comment on the matter and will update this post if we hear back.
Update: It now appears that the service is down for both OS X and iOS users.
Update 2: As of 6:15PM ET, it seems that the iMessage service is back up for the majority of users on both iOS and OS X, though we are still getting reports that it is still down for some.