Though not really answering your question, there used to be a "modal like" way to write Japanese on cell phones before :
The first letter you hit was a conson let's say K, and then, and then the next key you would hit would have the role of a conson. (Having two conson in a row is impossible in Japanese)
Though it was main a few years ago, today it's only used by people who really want to hit fast.
