Tell us about yourself!
I'd be more inclined to believe a simpler explanation - that the ultrasound excites nerves at the same frequencies as Flanagan's original neurophone does and frequency-modulates the affected nerves to deliver an audio signal that somehow is "heard" by the brain's auditory cortex.
milliamps (~10) are the range where you start seeing the risk of cardiac arrest and other physiological damage through the skin. If the signal in the low-microamp range, yes, I'd agree that we're talking about a medically safe signal..I'm thinking that one of those over-the-counter TENS units might be a good point to start with for a more sophisticated neurophone, but don't think the actual signal processing hardware can be adapted. You'd have to disable that and just use the amplifiers on board (if indeed, they are discrete from the signal generator chip) to drive the electrode pads that come with the TENS unit.