http://www.engadget.com/2014/02/11/leaked-windows-phone-8-1-developer-build/
leasantry:
MS is raising expectation so much, hope they don't disappoint last minute saying that XYZ phone won't upgrade to WP8.1Windows Phone 8.1, which according to the provided SDK documentation has been relabeled WinPRT, also ushers in a critical change to SD card functionality that should please longtime critics of the platform. Namely, users can now install apps to SD card and not just sideload from it, thus freeing up internal storage. Bing apps are now apparently pre-baked into the OS, as are a trio of "sense" apps to monitor battery power, data and storage. SkyDrive, as previously reported, has been rebranded to OneDrive and there's even a new Music app on deck (said to resemble Xbox Music) to replace the former Music+Video. One of the more surprising changes Microsoft's made to the Windows Phone platform focuses on how it handles SMS receipt and delivery. With WP 8.1, text messaging will no longer be restricted to the native SMS app. The messaging settings submenu includes the ability to specify which third-party app routes that communication by default. Users expecting new live tile sizes will be disappointed since this update doesn't include any options beyond the three already available in the OS. Although, there are apparently plenty of minute cosmetic overhauls packed into the 8.1 update. Among these are new default transitions for moving between apps and homescreens, a navigation bar with color settings to match backgrounds or accents, gestures to hide and reveal the onscreen navigation buttons, as well as the addition of Windows RT's progress ring. Back button functionality now also falls in line with WinRT in that it simply sends applications into a 'suspend' state, as opposed to terminating them. To actually close apps out, users will have to enter into multitasking view and swipe down to end the process.