I don’t actually use my phone a whole lot for placing telephone calls. After getting an iPhone 7 about a month ago, this morning I received my first voicemail message on iOS 10. I was surprised to find the voicemail message audio auto-transcribed to text, and transcribed very well at that.
While an obviously useful technology, I presumed that the voicemail had been processed by Apple remotely at some server farm, as most current hip artificial intelligence applications run on servers rather than on clients or local computers, and that this was yet another affront to individual privacy.
Happily, I was mistaken. According to an Apple support article on using iOS 10 voicemail transcription, all transcription is done local on the iPhone device itself. If the transcription was done poorly, you can optionally send it to Apple for the purpose of them improving the transcription system, but otherwise, it appears that the transcribed text is in fact private to your phone!