Apple’s new Siri assistant has really revolutionized the way in which we interact with mobile devices using our voice. It’s no wonder, then, that rivals are scrambling to introduce their own alternatives. Google already has one for Android, according to some reports, called Majel, and it’ll debut during the first quarter of 2012.

Say hello to Voice Actions. She’ll say hello right back.

Voice Actions is a basic Siri alternative, available right now in the iOS App Store.

Despite the fact that Siri’s guts are in a billion dollar data facility in North Carolina somewhere, the iPhone 4S can actually be used to voice control an old Mac 512K.

Want to test out iOS 5 but don’t have a developer account? No worries: a new vulnerability makes it pretty trivial to upgrade to iOS 5 on any iPhone.

Be careful, though… rolling back to iOS 4 if things go south isn’t officially supported. This is for pros only, and there’s a lot that can go wrong.

Amongst other rumors about iOS 5 that somehow just disappeared into the ether come yesterday’s WWDC 2011 keynote was the advanced Nuance-powered voice control features that has been reported extensively over the past few months. The only mention of voice recognition was a throwaway line on a slide: “Option to speak text selection.”

Is that it? What happened to the voice control that we were all promised? Don’t worry just yet: according to a couple of prominent sources, Nuance-powered voice control is still coming to iOS 5.

At the weekend, the Wall Street Journal reported an intriguiging detail about the upcoming iPhone nano: the new iPhone would feature “voice-based navigation.” (It will also be streaming-only, according to our report).

Could this be true system-wide voice control, as programming legend Bill Atkinson predicted at Macworld?

As we previously reported, Atkinson said it’s clear that iPhones would one day be controlled by voice, but he predicted the development to be several years away — two to ten years, he said.

But Atkinson reminded us we can get a sneak peek at the technology if we tune into Jeopardy! tonight. The history-making show features IBM’s DeepQA Project Watson supercomputer versus previous champions, Ken Jennings and Brad Rutter.

It’s likely to be a first public demonstration of the kind of natural-language and real-world knowledge technology to make it work.

“When we see computers interacting with a natural language interface, people are going to want it,” Atkinson said.

“I’d ask you all to watch Jeopardy on February 14,” he said. “It may be a momentous occasion.”