Interestingly, if you break your iPhone on vacation and buy a phone that is not an iPhone so that you can still be contacted until you get home to your favorite Apple Store, you are also losing messages, assuming you forget to go through Apple's iMessage deregistration system. Really the design of iMessage is the problem.
If you register your phone number to iMessage without any other iMessage receivers and then turn off that iPhone, messages sent for an extended period of time will continue to be queued for delivery in iMessage. In order for other iPhones to start falling back to SMS you need to manually deregister. In Google Messages and other RCS clients, by default it will give you a "Message not delivered" message indicating your message never made it to the handset. You then have an opportunity to manually resend that pending message via SMS. You can disable this behavior though if you prefer to use the two-check delivery receipt information to determine when your message hits the handset.
While neither mechanism is perfect, the RCS model treats lack of delivery to the handset as a potential problem, whereas iMessage ignores it. iMessage assumes your phone is just off, which for most people you are texting, is an unlikely scenario.
For users who actively turn off their device for certain activities, you have the opportunity to just wait, and when it arrives the error will clear, or send it as SMS and it will pick it up when the handset does turn on. But while the message is in flight for any length of time, the UI treats it as "something is wrong".
This means whenever you return to the conversation to check for a response or text more, you'll be reminded strongly that the message never arrived for them. And you always have the opportunity to resend on SMS during that time.
Not OP, but I believe it falls back to SMS if there isn’t a response from Apple’s servers, not the end user’s device. In this scenario the iMessages are sitting there waiting for a registered device to check in to send them to. (Same thing that happens if your battery dies. iMessages go into a void until some place to deliver it to.)
Yes it does fallback. There are two situations where it does so
1. The sender cannot connect to the imessage server
2. The receiver does not connect to the imessage server, on any of the devices registered to receive at that particular address.
I know both methods happen since I didn't used to have data and I would receive SMSs when someone sent me an imessage and I was out and about.
I think that's if iMessage can't reach Apple's servers. Otherwise that wouldn't make sense; simply being without a cell/wifi signal, or having your phone off, for a few hours, would mean anyone messaging you would be sending a bunch of SMS fallback messages.
It is how it works, after a certain timeout where it can't be delivered to a device it will fallback to SMS. The exact length of the timeout is not public.
No the idea is that you forgot to deregister yourself while still on vacation and using a non-iPhone, the Apple Store bit was the "get a new iPhone" part after your vacation is over.
And what you link to is what I meant by
> assuming you forget to go through Apple's iMessage deregistration system.
