[likpok]

It depends on what you're trying to do. Most phones I've used can be operated with one hand, blindly, to do common tasks (raise/lower vol. silence call).

The biggest problem, though, is that modern portable devices /need/ the expressiveness of a keyboard. Which is why devices like the Blackberry, the sidekick, etc. took off.

The touchscreen changes some of that, but, from what I hear, it doesn't quite work as well.

[markessien]

Why do they 'need' it? If voice recognition were completely perfect, they would not need it.

[rplevy]

The power of editing and revising printed text with a keyboard is not something that can be easily duplicated using voice. Consider trying to write code in this way. It's easy to say words but faster to type when you need custom spellings and editing words at a character level. It seems awkward to have to edit text with speech (easier to type something like C-space down down C-s quote . right C-space C-k M-x end-of-buffer C-y than to say it). Maybe some combination of keyboard and voice would work. Voice is not be ideal for a workplace situation, unless it is subvocal silent speech, which it sounds like is a technology that is almost ready.