iPhone 6, Sprint network, upgraded to 9.0.2 a few days ago, and have been having sporadic issues where the iMessages would go through as texts, but I chalked it up to the other person's network. Today, however, it started happening with everyone. After resetting the network, resetting EVERYTHING, doing the whole airplane mode thing, toggling iMessage on and off, signing out of Apple ID in messages, etc. Basically, every "tip" I could find online, I found one person who said that their iMessages went through fine to the others who had upgraded to 9.0.2, but was being weird with anyone who hadn't upgraded.
This has been consistent for me. Everyone I asked who has upgraded, the iMessage works fine.
For everyone else, it either sends as an iMessage at first, without saying "delivered" and then later when I open the thread, it has changed to say "sent as a text message," or it's just sent as a text message to begin with. The weird part is, the person on the receiving end says it comes through to them as an iMessage. even showed screen shots to each other. In a few cases, I've even had it say "delivered" but when I re-opened the message thread, it had changed to "sent as a text."
The only people I have success sending iMessages to reliably are those who have upgraded to 9.0.2.
This is really annoying and makes me concerned that my messages might not always be going through, or that I'm not receiving messages in timely matter, or even at all.
I haven't been thrilled with some of the iOS 9 changes, but this takes the cake.
I agree that there should be a another fix or, even more preferable, a rollback until they can fully fix the iMessage issues.