The app comes courtesy of XDA, as usual, and it took a little bit of finagling to get it working on my phone. Namely, I had to paste it into an area accessible only with root, and then change the permissions on the file. Nothing too bad, if you have dealt with this kind of thing before.

This is quite the feat, given that my test hardware is a Samsung Captivate, the runt of the original Galaxy S line.
But using S-Voice isn’t nearly so magical as Siri. It feels more like Samsung took the existing voice commands, decreased the accuracy of the translation, and added a few more actions to the list.
To send a message, for example, you have to say something like “text Katie message are you free for dinner?”, which is the actual example they give. Apparently you can also use it to open apps, but I’ve never successfully had it do that for me. Basically, you can’t expect nearly the flexibility you have with Siri. You can’t ask for restaurant recommendations, for example, and just about the only fun easter egg happens when you ask it what the meaning of life is. But hey, at least you can create alarms and calendar reminders, something sorely missing from voice actions.
To say I’m underwhelmed would be an understatement. This feels like a warmed-over version of Google’s Voice Actions, one that wasn’t even implemented well. If the rest of the device works as well as S-Voice does, well, the Galaxy S 3 is going to be a dismal failure.