What this tells me after a cursory read is that while this is in theory possible, both hardware limitations and software ones limit the maximum sampling frequen

What this tells me after a cursory read is that while this is in theory possible, both hardware limitations and software ones limit the maximum sampling frequency of a gyro. As such, it is going to be incredibly difficult to recover any usable information. There are some indications that using the right classifiers might improve results here, but their 10% accuracy for identifying digits is about equivalent to random guessing. Expand the corpus to include all of colloquial English (and potentially all other languages) and that precision drops to a very low number. With that said, someone crafty may be able to convince the OS (most likely Android, in this case) to turn up the sampling frequency to 8kHz -- that same sampling frequency as POTS -- and there might be a real risk of this technique used as a data gathering technique (or at least a way to drain your battery really fast).