To switch between xt9 and abc input modes on the Dash, hit [alt], [space].
xt9 is an completion-assist engine for text input. If you start typing "da" it will suggest da, day, damn, dan etc. This can be helpful, except that its behavior can be erratic. In some programs, space selects. And in some programs, the currently selected word is the first suggestion, not the letters you've just typed. This means that you'll hit space on "da" because you mean to insert a space, but instead, since the first selected word is day, day gets inserted, and no space gets inserted since it was used to select. You then end up backspacing, or always glancing at the screen to see what's selected before hitting space, or hitting space space to select and then insert a space. If you switch to abc mode, you can just type, and the letters you push are the letters that show up. Nice and simple.