A "leaked" Microsoft document has emerged suggesting Windows 7.5 "Tango" will be released late in 2012 alongside Nokia's fabled Lumia 900 smartphone.

Tech site WMPoweruser alleged that it had received a "leaked roadmap" document proving Microsoft's intention to roll out the Tango update around October 2012.

Rumours followed previous speculation that Nokia and Microsoft are set to unveil the new Windows Phone Tango-powered Lumia 900 at 2012's CES - indicating a Q2, 2012 release date.

The conflicting rumour stemmed from Mobile Magazine, which reported it expected to see the new citrus-flavoured Windows Phone update make an appearance at next year's CES trade show.

Though no solid information has been given by Microsoft the upgrade to the company's Windows Phone 7.5 Mango OS is expected to host a slew of new features. Chief among the expected changes is added support for smaller screens, smaller chassis sizes and LTE - a fancy term for 4G.

Lending credence to Mobile Magazine's report, a further rumour from BGR emerged earlier suggesting a Q2 release.

BGR alleged it had been told by a trusted source that the 900 would hit American stores in "early" 2012 - right about the time CES is set to kick off. BGR went on to allege that the new Windows Phone would run on a future, unconfirmed, "Tango" version of Microsoft's mobile operating system.

Unfortunately, for those eager to see Nokia's next entry into its Windows Phone series of devices, the company has issued no official information on the Lumia 900. When asked about the rumours Nokia representatives said: "We do not comment on rumour or speculation."