At an event during the CTIA show in Orlando, Fla., yesterday, Sprint and HTC revealed the HTC EVO 3D, a smartphone that offers glasses-free 3D visuals via its 4.3-inch display.

But the device is one of many 3D phones that have been announced in recent months. In February, LG revealed its Optimus 3D, which the company recently renamed the LG Thrill 4G. Like the HTC EVO 3D, the Thrill 3G also offers glasses-less 3D, allowing for both 3D video recording and playback.

Last November, Sharp launched its own pair of 3D Android phones. The Galapagos 003SH and 005SH, which run on 1GHz CPUs, can render 3D images on their 3.8-inch screens. The devices, while not released outside of Japan, were the first of multiple 3D phones that have appeared in recent months.

Sharp is widely believed to be the manufacturer behind the special 3D screen in Nintendo’s 3DS. Using a parallax display technology, the 3DS’s screen splits the image on its screen into different images for each eye, creating a sense of depth. Sharp’s parallax screen also solves some problems that had plagued previous 3D LCD technology, doubling the brightness and improving image quality.

Most significantly, however, Sharp’s 3D screens don’t require special 3D glasses. This makes them ideal for mobile devices like smartphones and the games consoles, but it also makes them ill-suited for use on larger screens like televisions. This is evident in many of the early reviews for the 3DS, which has what some reviewers call “a narrow sweet spot” outside of which the 3D image is disrupted.

Mobile 3D devices also face issues over content, which manufacturers have taken notice of. The EVO 3D will be the first 3D phone will Blockbuster's On Demand mobile App pre-installed. With the app, the EVO 3D will avoid one the major concerns surrounding 3D devices - the lack of content to play on them. Nintendo reached a similar deal with Netflix, which Nintendo announced earlier this month at the 2011 Game Developer’s Conference.

But a major source of mobile 3D content may be users themselves. According to HTC Americas President Jason Mackenzie, the “real magic” in devices like the EVO 3D emerges when users capture their own videos and pictures. Nintendo has also hinted at similar functionality in the 3DS. “I think it will be fun if we’re able to include video recording capabilities with future updates,” said Nintendo president Satoru Iwata.