Oh man. That would be incredibly cool. I use dictation all the time on my iPhone, for example I'm dictating this comment right now. It's just almost always faster than typing. But I'm never going to dictate anything at the office or on public transportation. But if I could just hold the phone up closer to my lips and have it transcribe just as well while I "talk" silently, that would be really interesting. And in the same way we've completely normalized people who seem to be talking to themselves, until you realize they're having a conversation over their earbuds, we'll completely normalize people silently mouthing sentences to their phones. What a weird but fascinating idea.

This so strongly reminds me of parts of the Ender's Game series, as well as some of Vernor Vinge's works. (I won't say which ones to avoid potential spoilers.)