Though perhaps by accident rather than intentionally, Microsoft has finally revealed Windows Phone 7.8's launch date: 31 January.Said date comes courtesy of Microsoft's Columbian arm, with the giant taking to its Facebook page for Windows Phone in the region to state that the update will begin rolling out from the end of the month.That doesn't mean all devices will get the update  which brings Windows Phone 8-style functionality to existing Windows Phone 7 handsets  at the same time, however.Indeed, Microsoft's post seems to suggest that its launch will be staggered across the entire first quarter of 2013. That would follow the model set by previous Windows Phone updates, which have typically taken a month or more to reach all handsets. Microsoft Russia has previously suggested it will be up to manufacturers to decide if their handsets gain access to Windows Phone 7.8, with Nokia equipping devices currently shipping to retail with the update.Interest in the update is certainly high - articles on Windows Phone 7.8 topping PocketGamer.biz charts since the start of the year - though Microsoft's Redmond base has refused to comment on its debut.[source: The Inquirer