Remember when phones sported plastic covers and not glass? Things have certainly changed. The shift arguably began when Apple (AAPL 1.66%) hired Corning (GLW 0.44%) in 2006 to design the display for its first iPhone. Corning has since been Apple's primary supplier for displays on its iPhones. But with new demands from smartphone manufacturers, it is more important than even for cover glass suppliers to innovate.

iPhone 5c. Apple currently uses Corning's Gorilla Glass in for its iPhone displays.

While the main question for smartphone manufacturers about glass just a few years ago was simply: Big or small? New questions have now found their way to the forefront. Curved or flat? Sapphire crystal or Gorilla Glass? Home button or not? And now a new rumor from The Korea Herald suggests both Apple and Samsung may be ditching bezels on the edges of its new smartphones, opting for curved glass on the edges instead -- yet another move by smartphone manufacturers that is putting increased pressure for innovation on cover glass suppliers.

Ditching bezels?
A new report from The Korea Herald  asserts that both the Galaxy S5 and the iPhone 6 will sport a bezel-free display. Furthermore, the Galaxy S5 will reportedly have fingerprint-scanning technology built in to the bottom of the display on the left and right sides. This report goes contrary to earlier speculation that the Galaxy S5 would have scanning fingerprint-scanning technology on the entire screen. The Korea Herald says full-screen fingerprint scanning technology will still come to market, but not until the later half of 2014.

The glass war heats up
Pressures for innovations like these are prompting manufacturers to explore different glass technologies, and sometimes ditch suppliers. Apple, for instance, has recently contracted with GT Advanced Technologies to produce sapphire glass for future Apple devices. Based on reports of massive orders of equipment for the factory, there is speculation that Apple will eventually use Sapphire glass as the display for its iPhones. Since Corning currently provides the displays for Apple's iPhones, this would likely be a setback for the company.

While there's no indication yet that curved bezels specifically would provoke Apple to ditch Corning, the heated competition and exacting demands from phone manufacturers means that supplier innovation is more important than ever.

Already the wearables market looks like it will be split between glass technologies. Apple may be planning to use sapphire, but Corning's glass is satisfactory for other wearable manufacturers. In January, Corning announced that its new Gorilla Glass was chosen as the cover glass for the new Pebble smartwatch.

While sapphire glass is known to be both more durable and scratch resistant, Corning's Gorilla Glass has advantages too. The company cited these advantages in the press release announcing the contract for the Pebble smartwatch, obviously aiming the words toward GT Advanced Technologies' alternative glass:

Corning Gorilla Glass, well-known for providing durability and scratch resistance in smartphone, slate and laptop applications, is now bringing those features to the smartwatch category. Compared with sapphire crystal, Corning Gorilla Glass is lighter weight, requires significantly less energy to produce, and transmits more light for better optical clarity.

Apple apparently values durability and scratch resistance more than the benefits Corning cited, since it is reportedly using sapphire glass for the display in the iWatch.

The big takeaway for investors is that it's tough to choose the winners in a fast-changing market with intense competition. So investors in the space should either have an excellent understanding of the glass market for mobile devices, or they should avoid the space entirely.