Here's an interesting post from NYT regarding voice commands and recognition and Apple's Siri. As we well know, Apple's Siri is a significant addition to the mobile experience even if it's not ready for prime time. I've used it often and it's good enough for the most part.
However, many have suggested that Google, which doesn't have a direct competitor to Siri (yet), offers a better voice recognition advantage.
The reason is simple: Google offered a free Google-411 service and voice search that essentially allowed Google to capture tons of voice requests years before Siri came onto the scene, even before Apple bought Siri.
It'll be interesting to see if we'll see Siri evolve with better artificial intelligence that what we have now and what we saw at Apple's WWDC demo when iOS is released. Right now, there is a lot of apps in both Google Play and iOS app store that compete with Siri that delivered results that is just as good as Siri (in some cases, better).