I've already learned Dvorak for full-keyboard PCs and two different input methods (Graffiti and TapType) for my PDA. My next PDA will likely have either one of those thumb-QWERTY keyboards (which I loathe; they are easily the worst of all possible input methods) or a Graffiti/Fitaly combo. I eschew the phone input not because I don't think I can master it -- what's to master? it's a phone keypad! -- but because trying to enter text on a phone kepad is inherently annoying and stupid. If I have to choose between replying to a message right this instant and waiting until I can reply using a proper keyboard, I will wait.
Now if only I could get TiVo to listen to a wireless infrared keyboard rather than requiring me to spell out what I'm looking for with that obnoxious point-and-click alphabet, as if I were a paraplegic, life would be good.