I use one. I don't think that it would be a good substitute for this use case. You can try and do steno on your phone with Dotterel but it's not a good experience - you're better off using a swiping keyboard. I've not used a T9 system in my life, but I can imagine that it's a system that would let you input anything just typing with your thumbs. To have a good time doing steno, you have to exercise all of your fingers on both your hands. That's not quite so nice on your phone.