The Airplane mode remedy has been advised by several iPhone users (through forum posts) who have experienced identical difficulties with iMessage, including the waiting for activation error. This may appear strange, but it appears to work for a number of individuals who are seeing this problem. The following is how it works:

1. Go to your iPhone's settings menu.
2. Look for Messages at the bottom of the page.
3. Disable or turn off iMessage and FaceTime under Messages.
4. Swipe up from the Home screen to access the Control Center.
5. Toggle Airplane Mode on or off with a tap. Wi-Fi should be switched off or deactivated.
6. Your iPhone should be restarted.
7. Turn on Wi-Fi after the restart.
8. Return to Messages and then enable iMessage.
9. If you see a message that reads, 'Your carrier may charge for SMS,' touch OK to continue.
10. Turn off iMessage and then on again after a few seconds.