iMessage on iPhone Sends as Text Message Only
I've got a problem with iMessage on my iPhone that has me at my wit's end.
Until very recently, I've had no problem with iMessage. It has sent messages to other iOS users within the Apple architecture (blue balloons).
Now, when I type in an iMessage to another iOS or iMessage for Mac user on my iPhone, it initially turns blue as it starts to send. Then, a red exclamation point appears with the words "Not Delivered" appearing then the bubble turns green and it says "Sent as Text Message."
I've tried re-setting iMessage and Facetime by turning them off, re-setting the network connection, then turning iMessage and Facetime back on. I've also restored the iPhone by backing it up, restoring it, then restoring the backup from my Mac.
I haven't installed any iOS updates (I am current at 7.0.4) and I haven't installed any new software.
Any ideas on how I can get iMessage working again? I' don't want to use text messages for my communication with other iOS users!
Thank you!!
iPhone 5, iOS 7.0.4