If you did all of the analysis on device, even quite cheaply, you could just transcribe key words and phrases into a text file and upload that. That would only be a few kilobytes of data tops per day of unique words and phrases, I should think. And if you've ever tried to monitor data usage on an Android phone, you'll know that the monolith of Google Play Services phones home all the time with all kinds of pings and datapoints, so it wouldn't be hard at all to upload that data.
