James Martin/CNET

Two years ago, the term "3D phone" would more likely fill phone-watchers with anxiety than excitement, as ghosts of the ill-fated LG Thrill and HTC Evo 3D come home to haunt.

But unlike 2011's efforts, which focused on 3D photography and gaming, companies' new-wave 3D vision ranges from gestures and navigation to a 3D interface effect. Google has Project Tango, Microsoft has apparently inherited Nokia's "McLaren" R&D, and now Amazon has launched its Fire Phone , complete with added cameras for creating a range of 3D effects.

With Google's annual I/O developer conference around the corner on June 25, and Microsoft's lab hands hard at work on future phones, the time may be right to prep your peepers for some extra dimension.

3D navigation and controls

Microsoft is rumored to be working on a "3D" Windows phone that lets you control the device the way you would Microsoft's Kinect gaming system for Xbox. But don't start envisioning yourself choreographing elaborate gestures to dial up pizza delivery just yet. At this point, it's probably better to think of the new technology as a navigational aid that taps into physical motions when your fingers aren't touching the screen, and uses your hovering finger when they are.

For example, sensors around the phone might recognize that you're laying down while you read, and temporarily lock the screen orientation so your contents don't accidentally flip around. Sliding your finger along the phone's spine might zoom in and out, according to The Verge, though it's also easy to see how context-awareness could also let your walking digits scroll the page up and down in the browser, and raise or lower the volume when you're on a call. Flipping the phone over or pocketing it could disconnect a call, and a deliberate wave of the hand over the screen could shelve notifications.

The project is said to contain an interface element as well, which is being called MixView. Hovering your finger over a live tile on the Start screen could cause it to pop up other options that you could select without physically tapping the tile; for instance, pulling up headline stories or a contact's phone number or email address. Tech site WP Central describes it in more detail here.

Since these scenarios require more complex hardware and software to work, the first phone, allegedly code-named McLaren, has to have all the right sensors, presumably multiple cameras for tracking, as well as a depth sensor -- just like the Microsoft Kinect. Although Nokia had reportedly been working on McLaren for years before Microsoft picked it up, the company's experience with Kinect's gestural gameplay fits in well.

Now, smartphone-makers have worked with gestures for years, and most current smartphones include some sort of motion awareness that can respond when you shake it or flip it over or raise it to your head. Samsung has gone a step further in some flagship phones and tablets by letting you hover your finger (or stylus) over, say, tiny thumbnails and drop-down menus to pop open larger previews.

Via WP Central

The 3D Touch program could certainly simplify some interactions with your phone, or streamline it by stripping off buttons, like the volume rocker. Likewise, gestures can be tricky if they require users to learn a new navigational system without any button backups, two lessons from the gesture-heavy WebOS and even lesser-known Yota Phone .

Since a gesture-navigated device has to make sure you're really intending to complete a task and not just randomly moving around, some motions could also wind up taking longer to complete than if you just mashed your fingers on the screen. To really give Windows Phone an edge over Android and iOS, Microsoft would have to get 3D Touch just right.

3D interface moves with you

Off-screen navigation may be one direction that 3D smartphones are headed in, but as Amazon demonstrated with its Fire Phone, 3D can also refer to the way that an interface looks and responds to you.

Now playing: Watch this: Amazon's new "3D" Fire Phone turns heads

3D wallpapers, mapping, gaming, and shopping through Amazon's gargantuan shopping portal are the major ways Amazon is integrating a more immersive look and feel on its phone, thanks to the four tracking cameras on the phone's front.

A number of home-screen replacement apps on Android impart a 3D look and feel to a phone's interface, and some of you may even remember Hitachi's Wooo H001 from 2009, with it's world's-first 3D interface (video). Amazon's skin, however, is much richer and more advanced than the efforts of five years ago, and several added motion controls go beyond passive viewing.

Real-time 3D modeling

Then there's Google. The 1,000-pound gorilla rockets into the 3D mobile world with Project Tango, a massive effort to cram cutting-edge 3D tracking and computer vision into mobile phones and tablets.

The reference tablet that Google just put on sale for developers includes a 120-degree wide-angle camera, a motion tracking camera, and a depth sensor, which together will lead to all sorts of applications for 3D mapping, indoor modeling, and augmented reality. The sensors make a quarter million 3D measurements every second, Google says.

"Our goal is to give mobile devices a human scale understanding of space and motion," Tango's project lead Johnny Lee said in Tango's introductory video (below).

Google has made some prototypes to illustrate what developers can do with Tango, like create a gaming environment mapped to a user's living room, so that the game character walks when you do. Likewise, visually impaired people could benefit from auditory cues as a device running Project Tango could help circumvent obstacles in real time.

Preparing for a 3D world

It's clear with these strong rumors and big initiatives that "3D" phones are making a comeback, this time with far greater sensors, much more sophisticated software tools, and processors powerful enough to resolve graphics on the fly.

At this point, all three avenues have their promise and potential, but, like Samsung's ballyhooed eyeball tracking feature in the Samsung Galaxy S4 and wireless charging in any device, all that potential could still fall short of truly useful things we use every day.

For Amazon, Microsoft, and Google, translating their "3D" work into the most import space there is -- the 3D phone or tablet in your hands -- is a step toward turning mobile devices into even more potent and indispensable tools.