By default the Calendar applet uses normal character editing mode (no XT9 mode) on the Description field.
Well, this is not really true, however. While entering words, they are still underlined, like in XT9 mode. This "hybrid" mode keeps the user from editing the text because cursor keys don't work. Just the [BACK] key is available.
I'd like to suggest that Calendar text fields all start in XT9 mode by default. Moreover, if these text fields don't contain any text when entering them, XT9 mode should automatically start in Capital Letter mode.