Siri, a tiny voice search startup, confirmed that Apple acquired them today. Siri describes themselves as a kind of Internet-connected voice search option--"You can ask Siri to find a romantic place for dinner, tell you what’s playing at a local jazz club or get tickets to a movie for Saturday night." This goes way beyond "dial Mommy." And why does Apple care about this? Because Google is amazing at it.
Apple's current voice search on the iPhone OS is near-archaic and generally worthless. It's limited to searching the stuff already in your phone, like contacts--your Motorola Razr from 2004 had about the same functionality. But the iPhone can and should do better. Just look at Android, which uses Google search extraordinarily well.
Voice search is built into every Android phone that runs Android 1.6 or later (which is just about all of them). Every Android phone has a search button on its face: tap it, and it'll start searching the internet, your contacts, music, videos, YouTube, news, apps, and more. Press and hold, and you can just start speaking--it'll search everything by analyzing your mush-mouthed mumbling. It's startlingly good, even for someone like me who apparently can't speak properly (I can't tell you how many times restaurant reservations have been made for "Ben" Nosowitz instead of Dan).
Siri goes a step further than Google Voice Search, connecting you to other services that might be able to help you. If you use Google and say "Thai restaurant near Haight-Ashbury, San Francisco," it'll give you Google search results. Siri might connect you with OpenTable or Yelp, saving a step.
As Gizmodo's John Herrman points out, Apple may or may not use Siri as is. They might use the developers to build their own system, or integrate their talents in some other way into the OS. But regardless, Apple's definitely making a move into voice search, at long last.