Physical discomforts of writing a novel on a smartphone aside, I am trying to wrap my head around trying to do the same with a device that needs T9 as input. I type slow on a touchscreen as it is, frequently losing my train of thought before I can get my whole comment out, the comments themselves often turning into meandering adventures in Fuzzy Logic Land as a result. I cannot imagine banging one out on a number pad, and I lived through that era, even working a job where cell phones were a no-no so we got pretty good at firing off quick texts without having to look at the keys. Short messages? Can do. Lengthy HN replies? Count me out.
Back in the T9 days, it was not uncommon for Japanese to be faster on a cellphone than on a keyboard.
The input algorithm used in Japan wasn't T9, but very similar to the kana-keyboard available on iPhones today, and the prediction (both kana-to-kanji and next word) was quite good as far as I remember.
I dunno until I learned to swipe on a touchscreen keyboard I was (and still would be) much slower there then with T9. I miss being able to text in my pocket without looking at my phone too...