Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Resetting Network Settings May Fix iMessages Not Working in iOS 7
While Apple's iMessage service has suffered from occasional outages, including a minor one documented on the company's System Status page earlier today, some users have been complaining of multi-day outages on their devices, suggesting that something more than a simple service problem may be occurring. Anecdotal reports have indicated that the issue may have worsened with last week's release of iOS 7.0.2, but reports of problems do date further back than that.
Some users have reported that turning their iOS devices off and back on fixes the problem, while others indicate that the solution has not worked for them. In our own testing with a device experiencing difficulties, the following steps appear to have fixed the issue (Note: this will cause your device to forget previously entered Wi-fi passwords)
1. Turn off iMessage in Settings > Messages
2. Reset networking settings in Settings > General > Reset
3. Reenable iMessage in Settings > Messages
Many users are reporting that these failed iMessages are also not falling back to traditional text messages as should occur when iMessage is unavailable. Instead, the iMessages simply hang during the sending process and eventually show as undelivered.