I haven't read all those messages. And so I'm sure someone must have come up with this idea before me. But when I read that Moffat interview and thought about, I hit upon a very uncharacteristic thing Sherlock did.

To quote from "A Study in Pink", "I prefer to text." He *called* John this time.

And I'll have to watch the scene again, but I wonder if he actually recorded that message beforehand. That the scenes of him speaking into the phone happened before John arrived on the scene and that it was a recorded message.