I agree it would be most useful on the phone, especially since it is supposed to work with a bluetooth headset.
Some people have commented about how awkward and embarrassing it would be to talk to your phone in public, and I more or less agree, but when I'm driving it's another world. Imagine being able to ask the time, distance to destination, directions to the nearest gas station, or even calling home all without that awkward need to remember exactly how to phrase the question. You can even dictate that random idea you had when you saw the Smart car cut off a two trailer truck loaded with cement blocks.
Too cool.
(and too much money to upgrade off contract, unfortunately.

)