Apple's iMessage is great when it works, but several recent outages haven't made it a little unreliable. Fortunately your iPhone can send any iMessage as an SMS text message when the service is down. Lifehacker reader Raj Nagra explains:
If you have a flaky mobile signal and try and send an iMessage it can get 'stuck' as your iPhone repeatedly attempts to send it using your intermittent data connection. You can override this behaviour when it's stuck in this loop by tapping on the message and a new option will appear allowing you to revert to good old-fashioned SMS.
You can also default to this action when iMessage is down by going to the Settings app, choosing the Messages tab, and choosing "Send as SMS" (as pictured above).