An iMessage, sent to someone who owns an iPhone, that can not be delivered to that iPhone, can never be "Delivered".
My wife inherited my old iPhone 3GS when I got the iPhone 5. She wasn't with a sanctioned iPhone operator in Belgium so she didn't get the APN settings OTA. I didn't think of checking them and setting them manually. So, she did not have an active data connection to her phone when she was out of the house.
We set up Messages at home when she was on Wi-Fi and Apple recognised her number as being linked to her Apple ID. Or is it iCloud ID? That dichotomy's another story... Now, when I started sending her texts they never reached her because during the day she is not at home, and Apple's servers couldn't connect to her phone.
Yet, whenever I text her Messages.app said the message was "Delivered". It got delivered alright, to her iPad that was lying at home, connected to our Wi-Fi network.
The reason must be that Apple's servers check for any device registered for receiving iMessages with the receiver's Apple ID. When it can reach one device it sends the message through and responds success to the sender. The sender has no idea to which devices the message arrived, all he gets to see is "Delivered".
Usually, when people send texts they mean to reach someone's phone. That's their primary target. If iCloud can sync it to iPads, iPods and Macs that's great but the phone remains most important.
With the above in mind (someone who has an unreachable phone but another device which can be reached) three situations can occur, one of which can be easily remedied, one is a bit harder and one where nothing can be done.
- Sending from iPhone. Apple should check the devices registered with the recipient's Apple ID, if it can reach the iPad but it can not reach the iPhone it should send the iPad message as per usual but also fall back to sending an SMS to the unreachable iPhone. Currently it does not fallback to SMS as soon as another non-iPhone device can be reached.
- Not sending from iPhone, but the sender has an iPhone. Apple should check the devices registered with the recipient's Apple ID, if one of them is a non-reachable iPhone it should then check whether the sender has a (reachable-via-data-connection) iPhone registered to his Apple ID. If so, then Apple can contact the iPhone and have it send an SMS to the recipient's phone to make sure the text gets delivered. Only if the sender has the fallback-to-SMS setting turned on of course.
- Not sending from iPhone and the sender has no iPhone. There is no way the message can be delivered to the non-reachable iPhone. I assume Apple does not have SMS servers in every country to make this happen on their behalf instead of using the sender's iPhone. But then it should not say "Delivered". It could say "Delivery failed." and show a popup with more info.
Solving situation 1 and 2 would help Apple get back on track with their "It just works" meme. It's a technical challenge, trying to get texts delivered any way they can. It's a interesting problem to solve. And when solved it would be magic. The user does not need to know how. It should just work.
Situation 3 would occur less frequently I think. People who don't have iPhones are less inclined to use iMessage.
With all of Apple's new services and software in the past couple of years... it has come to a point where a lot does not "It just works" anymore. More articles like this one will get written until they start fixing their software. Apple's hardware is drastically improving, their software department has been lacking.
I hope Apple will devote 2013 to doing nothing else but making things just work again.
Like it used to be.