By Darrell Etherington, GigaOM

The iOS 4.3 beta, despite being covered by Apple’s NDA, is leaking signs of new hardware and software features like a sieve. The latest find is support for multi-touch gestures on the iPhone. Apple is beta-testing these gestures publicly for the iPad in 4.3, but new evidence suggests private testing is going on for the iPhone, too. Might the presence of these features suggest a buttonless future for iOS devices?

According to Engadget, iPhone user Antoni Nygaard managed to activate the hidden multi-touch gesture features on his device using the iOS 4.3 pre-release software (as well as options to change the function of the iPhone’s mute button to a rotation lock, another iPad import). BGR also has screenshots of the gestures in action and the relevant Settings screen from a separate source. Nygaard’s demonstration of the feature in action can be seen in the video below.

Apple dampened anticipation surrounding the new gestures for iPad when it noted, alongside the release of the second beta of iOS 4.3, that these would not be included in the pubic release of the update, and were intended for testing purposes only. The gestures are even less likely to make it into a public 4.3 release on the iPhone, since they aren’t an acknowledged feature of the beta.

So why is the feature there? There are those who argue that it’s because Apple is going to get rid of the home button (that adorable one with the white rounded rectangle) in future hardware iterations of the iPhone, iPad and iPod touch. It’s true that the gestures replace navigation duties normally handled by the home button, making it possible to fully use the devices without ever touching such a button. But just because it can be done, does that mean it should?

The Case For

Gestures. The presence of the gestures themselves are probably the most convincing evidence in favor of a home buttonless future for iOS devices. Why else would Apple be testing not only app switching through swipes, but also the ability to bring up the multitasking tray and to return to the home screen, both of which taken together currently make up the bulk of the home button’s duties? Feature redundancy for its own sake isn’t one of Apple’s prevailing design principles. Ever look for the physical volume knob on a Mac?

Apple Hates Buttons. The latest iPod shuffle is a rare exception, but speaking generally, Apple has a tendency to do away with physical buttons if it can get away with it. The new nano is a prime example of the culmination of Apple’s design aesthetic: a touchscreen device with a thin bezel and no buttons on its face. Its simple swipe-back navigation works fine for the nano, but is obviously too limiting for an iPhone or iPod touch. Hence the introduction of more complex multi-touch gestures on devices that allow for them, like those mentioned above.

Smaller Devices With Bigger Screens. As Kevin pointed out, Apple may start thinking about equipping the iPhone with a larger display, and soon. Four-inch and larger screens have become de rigueur on many Android devices, and while the Retina Display still gives Apple a major advantage, a bigger Retina Display would provide a bigger advantage for video and gaming enjoyment. If Apple removes the home button, it can increase screen size without adding much or any bulk to the iPhone itself.

The Case Against

Usability. As you can see from the video above, things get pretty cramped when you’re trying to use four-finger gestures on the iPhone, assuming Apple doesn’t increase the overall size of the iPhone. Even putting that aside, gestures on both the iPad and the iPhone are far from intuitive ( as Jon Gruber notes), unlike a big, obvious hardware button sitting all by its lonesome on the face of the device. It’s hard to imagine Apple implementing a control scheme that requires an introductory walk-through as the default mode of getting around its mobile OS, which is the benchmark of simplicity in most other regards.

Accessibility. The home button has a very key function that probably isn’t used by most, but is important nonetheless. It can be configured to enable various accessibility options, including toggling VoiceOver, white on black, zoom modes, and having your device prompt you for a command. These are things that can’t or shouldn’t be rerouted to gestures, and that might prove confusing and awkward (read: less accessible) if attached to volume or sleep buttons.

Keeping Button Roles Clearly Defined. Apple would also have to reassign things like taking screenshots (currently done by pressing the home and sleep buttons simultaneously) and performing a hard reset (holding the home and sleep buttons simultaneously). Redirecting these functions to some combination of volume and sleep buttons would be a confusing change.

The iPod Shuffle. As mentioned, Apple went back on its buttonless iPod shuffle design after users and reviewers complained. The shuffle is a safe playground for testing new features like a buttonless interface, since consumers aren’t investing much in it and in Apple’s larger revenue picture, it represents only a very small part. It’s hard to imagine Apple taking the same chance with either the iPhone or iPad, which are revenue stars for the company and much more likely to leave a lasting bad taste in the mouth of consumers.

Home Is Where the UX Is

While Apple testing gesture controls at this juncture might indicate that the company is considering taking away the home button in future iOS devices, I think rumors of a buttonless iPhone 5 or iPad 2 are extremely premature. There’s too much at stake, and not enough potential return to justify a change like that. The home button is, in fact, at the core of why iOS devices are so easy to just pick up and use. Apple’s not going to go messing with its biggest competitive advantage and make adoption harder.

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