Microsoft almost lists Windows Phone 8.1's features on its website87
Either by mistake, or as a tease, Microsoft is now listing Windows Phone 8.1 next to Windows Phone 8 on the platform’s official website. Unfortunately, if you click the WP 8.1 link, which should lead to the “top features” of the OS, all you’re getting is a “Not found” page.
Of course, we already know most of the new major features that Windows Phone 8.1 will bring: support for on-screen buttons, a personal voice assistant called Cortana, a new notification center called Action Center, dual SIM support, and compatibility with new Qualcomm SoCs (including the Snapdragon 400 and 200). For more, here is everything we know about Windows Phone 8.1 thus far.
Microsoft could release Windows Phone 8.1 in April, after its Build Conference that takes place between April 2 and April 4. New hardware will likely appear at about that time, too, possibly not just from Nokia. But we’ll see what happens.
Update: The "Windows Phone 8.1" reference was removed by Microsoft today. So maybe this was a mistake after all.
source: Windows Phone via WPCentral