At Mobile World Congress Microsoft pulled the "rabbit out of the hat" and released a brand new mobile phone OS - Windows Phone 7 Series.

We managed to get a quick run through and some hands on time with the new OS on a reference unit, whilst also having a chat with some of the Microsoft bigwigs to get the lowdown on what's what.

Gone is the stylus and in comes a funky, sleek interface that looks to bring the Zune HD interface to a mobile phone near you.  

Windows Phone 7 Series is based around seven core hubs: Pictures, People, Browsing, Games, Music, Marketplace and Office.

The User Interface (UI) is totally different to both the company's own mobile phone operating system, Windows Mobile, and industry competitors like Android and the iPhone, since it brings with it a more interactive "live" experience. Rather than static icons in a grid, the phone is constantly showing interactive tiles that move, update and interact.

"The notion that a smartphone is all about apps isn't where we are coming from", Alex Reeve, the man in charge of Mobile for Microsoft in the UK told Pocket-lint.

Microsoft is hoping a connected interface to services like the Zune and its Xbox Live gaming offering, as well as a marketplace for apps and its Office services, will bring a more fluid approach to those who "want it all".

What that means in reality is that you'll be able to connect with your profile on the Xbox, sync with your contacts and generally treat the handset as an extension to your Microsoft life.

Expected to hit a phone maker near you in time for Christmas, there will be plenty of hardware and software restrictions to make sure that the new OS is consistent and exactly how you'll expect it to be. Operators and manufactures will be able to add elements to the design but there is "no flexibility to paint over the top" confirms Reeve.

The good news is that Microsoft has confirmed to Pocket-lint that the Zune "experience" will be heading to the UK in time for the launch, but that for the time being we won't be seeing the Zune HD.

Where do developers fit into all this? Not wanting to overwhelm with too much information Microsoft is for the moment keeping quiet, however it does say that it is keen on getting them involved in what they hope will be the vehicle to get them back in the "game".

Microsoft will be announcing further details on how developers will be able to get involved in March at the company's Mix event in Las Vegas.

We'll have plenty of news on this story as it develops on our dedicated Windows Phone 7 Series hompage.

Stay tuned.