In a move that few people expected, Microsoft have released an updates build of their new Windows Phone update, Mango, to developers through the Connect beta site along with a new beta 2 software development kit (SDK).

In a blog post the company announced…

“If that isn’t exciting enough, we’ve also pushed an OS update to the Microsoft Update servers this morning, allowing you to refresh retail Windows Phones that devs updated to Mango over the last month. If you previously updated.”

They go on to say that the new update is “Build 7712, which corresponds to today’s WPSDK 7.1 release. Before you ask (and I know you will, because folks started asking yesterday ), this build is not yesterday’s RTM build – it’s still a pre-release build. For RTM, you’ll need to wait for the official update like everyone else (more on the why later in the post).”

Anybody with the Mango update on their phone already, as I do, will be able to install the beta 2 update easily through the Zune desktop software without having to download an install any additional software from the Connect website.

The update isn’t the full RTM (Release to Manufacturing) version of the update.  In the post Microsoft explained why they’ve not provided this as the update went RTM yesterday.

“For the folks wondering why we’re not providing the ‘RTM’ version, there are two main reasons. First, the phone OS and the tools are two equal parts of the developer toolkit that correspond to one another. When we took this snapshot for the refresh, we took the latest RC drops of the tools and the corresponding OS version. Second, what we are providing is a genuine release candidate build, with enough code checked in and APIs locked down that this OS is close enough to RTM that, as a developer, it’s more than capable to see you through the upcoming RC drop of the tools and app submission. It’s important to remember that until the phone and mobile operator portion of Mango is complete, you’re still using a pre-release on your retail phone – no matter the MS build. Until that time, enjoy developing and cruising around on build 7712 – it’s a sweet ride, to be sure.”

This means that the very final developer SDK isn’t yet available for download and can be expected in the coming months.  The beta 2 refresh helps give developers a head start on apps for Mango.

The update to the phone itself takes only around 10 minutes and, having just installed it myself I’m off now to see what’s new