Oh, right. I agree with you on that front. I see it working this way:

If you are standing on top of a mountain, right now you can’t send anything.

With Apple’s upcoming announcement, you’ll be able to send an iMessage.

If you try to send a SMS, it just won’t go through—-same as it would today.

I hope Apple allows it for all messages, personally. But I could definitely see them restricting it, especially at the beginning.