Even that looks tedious:2-5 letters then selecting a character. To be able to get 140 words into a twitter page seems not a very practical goal, given that twitter is designed for about 30 and we so better than that with the two-letter version. Of course, the real solution is not to use twitter, etc. at all, but stick to media that don't have arbitrary (as far as is obvious) text limits. The point has always escaped me.
Or have a speech recognizer that takes tp to kanji at one end and kanji to tp - written - at the other. But then, why not telephone or at least eliminate the kanji?