Microsoft is planning a “major” update to the Windows Phone 7 platform codenamed “Mango” according to reports.

ZDNet’s Mary Jo Foley reports that the software giant is currently readying an update named “Mango” that could be shipped as Windows Phone 7.5. Microsoft has also codenamed Windows Phone 8 “Apollo” which is slated for release in late 2012.

The “Mango” update is supposedly larger than Microsoft’s January and/or February update. WinRumors recently reported that Microsoft is planning to unveil and detail a second Windows Phone 7 update in February at the Mobile World Congress. Microsoft’s second update will introduce enhanced developer controls for applications. Microsoft is expected to open up several new APIs that will allow for greater multi-tasking, in-app downloads and better customization for end users.

Foley explains that “Mango” will add Silverlight and HTML5 support to Windows Phone 7. Microsoft is also set to unveil its plans for a Silverlight update to Windows Phone 7 at Mobile World Congress. Brian Keller, Senior Technical Evangelist for Visual Studio application lifecycle management at Microsoft hinted at Microsoft’s future Silverlight plans in a recent Channel 9 interview. When questioned over any Windows Phone 7 Silverlight news Keller replied “I think we are saving those, for say another event. If only there was a massive event in Barcelona on mobile phones and or other events in the future.”

Microsoft is also working on a major overhaul of the Windows Phone 7 browser. In a job posting, listed in November, the software maker promises a “major overhaul of standard support and new approaches to make significant advances in performance, power consumption and bandwidth utilization.” It’s possible that part of the overhaul could be seen in the point release for “Mango”.