A month or more before its expected completion date, the next version of the Windows Phone 7 OS, code-named Mango, has been shipped to manufacturing. But it might be some months still before consumers can get their hands on devices based on the new system: Development tools for Mango won't hit a release candidate (RC) stage until late August and won't be finalized until September at the earliest. So, it's possible that an October 2011 launch—exactly one year after the initial Windows Phone 7 launch—is still the plan.

"The Windows Phone development team has officially signed off on the release to manufacturing (RTM) build of "Mango"—the latest version of the Windows Phone operating system," Microsoft Corporate VP Terry Myerson wrote in a blog post announcing the milestone. "This marks the point in the development process where we hand code to our handset and mobile operator partners to optimize Mango for their specific phone and network configurations."

Mango is a major update to Windows Phone and will ship on new devices this fall. But it will also be made available to all current Windows Phone devices for free, so existing customers will be able to utilize most of its new features and improvements. These include a dramatically improved email application with Conversation view and linked Inbox support, a new universal messaging app called Threads, multitasking for third-party apps, and a hardware-accelerated Internet Explorer (IE) 9 web browser, among other features.

Oddly, Microsoft didn't reveal the final branding for Mango, which is expected to be called Windows Phone 7.5, despite the internal version number of 7.1. And the company didn't discuss the schedule for any pending milestones, including the coming developer tool releases, the availability of the software for existing phones, and a possible launch event.

Availability to current handsets could be a bit tricky, given the lack of success Microsoft had earlier this year trying to deploy a handful of smaller updates. But hopefully Microsoft's wireless partners have learned from that experience and will allow customers to access Mango in a more timely fashion.