Apple Inc. (NASDAQ:AAPL) announced last week that this year’s Worldwide Developer Conference, or WWDC, the company’s annual developers’ meet, would be held from June 2 to June 6 in San Francisco with an in-depth look at the latest in iOS and OS X. While Apple has not revealed much about its plans for the event, many reports have suggested that iOS 8, the next major update to Apple's mobile operating system, could take center stage at the event.

With two months to go for the expected unveiling of iOS 8 at WWDC in June, 9to5Mac released a report Monday sharing new details about the upcoming iOS version, which is reportedly codenamed “Okemo.”

According to the report, both iOS 8 and the iPhone 6 are likely to feature Voice-over-LTE, or VoLTE, support, which is expected to improve call quality and efficiency. When the current LTE-enabled iPhones are used to a make a phone call, the actual call is placed over last-generation networks, such as 3G. Thanks to VoLTE, the calls can be transmitted over the same type of network that is used to process LTE data.

In the U.S., only T-Mobile US Inc’s (NYSE:TMUS) network currently supports VoLTE, while Verizon Communications Inc. (NYSE:VZ) and AT&T Inc. (NYSE:T) are said to be testing the technology for a rollout by the end of this year. If the carriers fail to implement the functionality within the scheduled timeframe, Apple could also delay iOS 8 support of VoLTE, 9to5Mac reported.

Although the current iOS 7.1 update significantly sped up animations and other system functionality, Apple is rumored to be testing iOS 8 with capabilities that are expected to improve speed across the platform even further. Sources have also revealed that the company is looking to improve the time taken to capture photos, focusing on the iPhone 6’s hardware components.

The iOS 8 update is also likely to bring a simplified Notification Center, which could only include the “Today” and “Notifications” views, while removing the “All” and “Missed” views that are found in the iOS 7.

According to 9to5Mac, the most significant feature that Apple is rumored to add to iOS 8 is “Healthbook,” which could combine various health- and fitness-related data from different applications and hardware accessories. The feature is rumored to also include an “Activity” section that can track steps taken, calories burned and miles walked by a user. And, there could be another section within Healthbook, called "Weight," which would track a person’s weight, Body Mass Index, or BMI, and fat percentage.

Click here for more details on iOS 8’s rumored features, such as a standalone iTunes Radio app, improved Maps app with better clarity and new features, optimized Preview and TextEdit apps, and inter-app communication among others.

iOS 7 Adoption Increases

Meanwhile, Apple’s updated App Store developer support page showed that the adoption rate for iOS 7 has reached 87 percent over the past one week, ending April 6. The numbers came seven months after the OS was released and two months before the expected unveiling of iOS 8.

In comparison, Google Inc.’s (NASDAQ:GOOG) latest Android 4.4.2 KitKat, which was rolled out in October, has been installed only on 5.3 percent of devices until now. The increased adoption of iOS 7 also led to a drop in the usage of iOS 6, which is currently running on merely 11 percent of Apple devices.

Check out the chart here:

iOS7-adoption iOS 7 adoption increases. Photo: Apple