I occasionally have a failed text message send, but only if I use SIRI (or whatever the voice dictation is in text messages.) I have the 4s.
If I type the message in, it's fine, but about 20-30% of the time when using dictation, it will fail. When I say fail, I mean when I hit send, the phone jumps immediately to the main screen without any warning. Acts as if I never even initiated the text message.
Haven't talked to anyone at Apple yet about this, as it is nothing more than an annoyance yet.
I believe it has something to do with Siri, since it only happens when using the voice commands.
(if this is the only problem this phone ever has, it's light years ahead of my (formerly beloved) Droid)