Amazon CEO Jeff Bezos. Alex Wong/Getty Images Apple, Amazon, and Google are at war over the future of personal computing, and now Amazon is taking the battle to its rivals' home turf: the smartphone.

All three are convinced that voice-controlled virtual assistants have the potential to transform how we interact with our devices. Apple has Siri, Google has Google Assistant, and Amazon has Alexa.

They believe that in the future, you won't swipe or manually fiddle with your device — you'll just talk to it, as you would another human.

It's a radical frontier — a change on par with the shift from the command line to visual operating systems like Windows. Whoever gets ahead now has the potential to define the next major era of computing.

The three have had slightly different approaches. Amazon, an early leader in the space, focused on its Echo smart speaker with Alexa. Google put Google Assistant inside its Google Home smart speaker and a few Android smartphones, while Apple's Siri was focused on the iPhone.

But now Amazon is coming for the other two and trying to invade the smartphone.

Amazon is creeping into iOS and Android through the back door

Voice-controlled computing promises to give everyone an on-demand, artificially intelligent personal assistant. Kempinski Hotels On Thursday, Amazon announced that Alexa would be available in its main shopping app on iOS, letting users shop for items, control smart-home products, and check the news and weather using their voice. A limited version of Alexa had been available for iOS via a standalone app — but this opens it up to far more users who otherwise might not have sought it out.

Alexa is creeping into Android phones as well. Amazon has teamed up with Huawei to bake Alexa to its Mate 9 smartphone, and the company is working with Lenovo-owned Motorola to integrate Alexa in some future Moto smartphones.

This all amounts to a kind of Trojan horse. Amazon failed to get a foothold in the smartphone sector. Its own phone, the Fire Phone, failed miserably. But as voice-controlled assistants become more common, if people see Alexa as the leading option, Amazon has a way to fundamentally control their smartphone experience anyway.

When it comes to voice-controlled computing, it's all still to play for

The Amazon Echo. Amazon But this is way, way bigger than just phones. Google and Amazon are now racing each other to bake their virtual assistants into as many devices as possible, such as cars and home appliances. Each is trying to get the kind of virtuous network effects that would reinforce usage and lock in its dominance.

Think about it — no one wants to have to switch between assistants that don't communicate with one another; they want one to follow them everywhere they go, from their phone to their thermostat. So the more places where a company makes its assistant available, the stronger position it's in.

And once a user is locked into an assistant, it's extremely difficult for them to swap, because unlike replacing a phone, you might need to replace the appliances in your house. That's just not going to happen, so the stakes are higher.

Microsoft's Windows won the PC wars, and Google's Android has dominated smartphones worldwide — when it comes to numbers, at least.

But with voice-controlled computing, it's still all to play for — and Amazon is determined not to lose out.