Siri has been lauded as one of the iPhone 4S's main selling points. The voice-powered personal assistant can be used for just about anything, although the feature is not exactly popular in some markets, particularly in Asia.

Apple's iPhone 4S launched in October last year to much fanfare. Even with the phone looking almost exactly like its predecessor, underneath, the smartphone is a new animal altogether. Among the main highlights: you can actually talk to it.

With Siri, the iPhone acts as a personal assistant. Users just need to speak commands in natural language, and Siri will process these without the need to memorize special commands and syntaxes. You can set alarms, look for directions, search for recipes and even dictate text messages or emails for sending. Reviewers have heralded Siri to be the killer feature of the iPhone 4S. But unless you're in supported markets, don't run off to the nearest Apple Store to buy your iPhone 4S just yet.

Is Siri Apple's Magic Bullet?

Siri might not necessarily be the magic bullet that Apple wants in all markets. In Asia in particular, personal voice assistants -- or so-called PVAs -- are useful, but adoption is slow.

Frost & Sullivan analyst for Asia Pacific Vikas Chanani says speech-powered assistants are a paradigm-shift in mobile devices. With apps like Siri, artificial intelligence is introduced in the mobile market, and "is a big leap toward how we'll come to communicate with devices, and opens up a plethora of opportunities for all of us."

He added that companies are working on how to integrated speech-powered technologies in other applications, such as computer games, cars, music players, TVs and media players, among others.

Other analysts are not so optimistic about speech-powered assistants, at least in the short term. Canalys' Tang Pin-Chen notes limitations to the technology. For example, some systems require a user to speak in a certain way, while ambient sound adversely affects some PVAs.

Apple, for one, has addressed the usability challenge, allowing Siri to accept commands based on natural speech patterns. One problem remains: Siri is limited to certain regions. China, for example, is among the biggest smartphone markets in the world, but Apple doesn't support Chinese at this time. Support for additional languages -- like Chinese, Japanese, Korean, Italian and Spanish -- has been promised for this year and might help encourage the use of PVAs in these regions.

Speech as the Next Great Thing in User Interfaces

Speech-enabled interfaces are not the only breakthrough in computing UIs. While Apple fans are confident that Siri will soon make an appearance in other Apple devices like the upcoming integrated Apple TV, other technology companies are trying other means to interface man with machines more naturally. Microsoft's upcoming release of a PC variant of Kinect with Windows 8 support is one example, with motion-based interfaces that hopefully make computing easier.

Motion-sensing technology has already made an appearance in console gaming. But will we soon manipulate elements on screen through flicks of our wrist and finger? Or will users prefer to talk to their devices? It's Star Trek vs. Minority Report, and we wonder which will prevail in mobile and desktop devices.