Windows Phone "Mango", the first major update to Microsoft's smartphone platform, has reached the Release To Manufacturing (RTM) milestone. Development has been completed, and the finished software has been sent to handset manufacturers and mobile operators for configuration and testing. Public release remains scheduled for fall.

Mango is a substantial upgrade, offering a wealth of features both for users—including Twitter and LinkedIn integration, Facebook and Windows Live Messenger chat, a hugely improved Web browser, turn-by-turn navigation, and rich Bing integration—and developers—a far more complete, capable API, limited multitasking, greater integration with built-in phone features—alike. The improvements all add up to make Mango a much more well-rounded and feature-rich platform than the original release, and do a good job of building on the foundations that the first release laid down: strong visual design, the aggregation of data, and the emphasis on making cloud services like Bing and Facebook an integral part of the platform.

Even as the software has been RTMed, many questions remain. Developers were given access to a prerelease late last month, but Microsoft is still working to get a finalized SDK and firmware version out to developers, and hasn't yet said when that will occur. Some features, such as the Twitter and LinkedIn integration, weren't available in the beta version, so the full extent of the integration and features for these remains unknown.

Even the final name and branding isn't known; the developer documentation describes Mango as version 7.1, but the beta firmware calls itself 7.5.

There's also been little said about hardware support. Mango will be available for every current Windows Phone device on the market, but a range of new devices—with new hardware specs—are expected to arrive with Mango. Microsoft has announced that Mango will include support for some additional processors and gyroscopes, but so far, that's the extent of what the company has said. Forward-facing cameras are widely expected, after analysis of the SDK showed evidence of software support for such a thing—but Microsoft hasn't confirmed anything of the sort. Even without a substantial hardware revision, new Mango hardware will certainly be shipping, however, including the first Nokia handsets, videos of which "leaked" onto the Internet last month.