Once again, I'm not bullish on voice controls as far as computers go - be it desktop, portable or handheld computers. In many situations (office, noisy environments) voice controls simply don't work well. And even when they do, typing is almost always more precise, and - if you type reasonably fast - sometimes even faster. I don't think that voice control applications are useless: there are many situations in which they work well. I'm just not bullish on the majority of users ever adopting the features that Vlingo offers.
Vlingo has already introduced a similar voice recognition software for the BlackBerry; our own Adam Ostrow was impressed with the service, so I guess it all boils down to what type of user you are. In any case, Vlingo's iPhone application is free, so it costs you nothing to try it out. Check out a demo video of the application below.