Even with 3G which I get great reception with it randomly decides its going to be slow or just not bother. This is over multiple iOS devices with multiple device restores. I just can't trust it.
It has had times where it was perfect but halfway through a conversation thread it'll just decide it's had enough and not work.
And then I use something like WhatsApp which has always been flawless and wonder what Apple are at.
I can't say I've notice it failing to revert to SMS. I never constantly watch my phone though, I press send, lock my phone and put it down.
I do that too. Waking it up later to realise it hasn't sent the message over any medium.
Oh right, strange. Can't that's ever happened to me.
It's always been iffy with me. 'Sending' but never getting a delivered notification. Sometime never actually arriving. Turned if off after a month of inconsistent service and don't miss it.
I don't understand this iMessenger, just feels like texting with a read receipt.. preferred BBM.