Just one problem: you can't have it yet.
Apple didn't say when Siri, which is still in beta, will be available, so it could be months before you're telling your iPhone what to do. Update: My mistake. Siri will be bundled with the
iPhone 4S, albeit in beta form. Plus, only iPhone 4S owners will be able to get in on the voice-powered action, owing to Siri's steep processing requirements.
If you don't want to wait, or don't want to buy a 4S, try Vlingo. Arguably the "original" voice assistant for the iPhone, this free app lets you accomplish a lot just by speaking. You can post updates to Facebook and Twitter, run a Web search, look up destinations on a map, place a call, and so on.
With Vlingo you can also compose and send e-mail and text messages. Until a couple of days ago (right when Siri was announced--go figure), you had to pay $6.99 for each of those functions, but Vlingo now offers unlimited e-mail and texting free of charge.
It's pretty cool, too. In virtually every voice test I tried, the app was uncannily accurate. (Funny side note: I told it to "Find apple orchards in ZIP code 48390," and Vlingo did--along with my nearby Apple store.) Check out Jessica Dolcourt's review of Vlingo if you want to learn more.
The big downside is that you have to launch the app manually, then press (or press and hold) the activation button. Apple doesn't allow you to reprogram the Home button to let a third-party app like this one assume voice-control duties.
And make no mistake: this is no Siri. It's not interactive in the same way Siri is, nor is it anywhere near as versatile. But until Apple's voice-powered "gal Friday" makes her debut, Vlingo is the next best thing. Plus, it's free, so no complainin'!
I'll wait in the comments for the inevitable remarks from Android users: "My phone can do this already! Nyah-nyah!" Yes, you're very special.