Microsoft employees are currently testing Windows Phone Twitter integration.

Several Microsoft employees have tweeted a variety of messages that appear to be test messages for Twitter Windows Phone integration. Microsoft had previously promised that Windows Phone Mango Twitter integration would be built in during the June timeframe so it appears the company is on schedule. External builds of Windows Phone Mango, available to developers, do not currently support Twitter integration.

It’s likely that Microsoft is testing the feature on an updated build of Windows Phone Mango or by using developer devices. Windows Phone developer devices allow owners to switch to Windows Live Internal domains to use dogfood features. WPCentral notes that the Twitter messages appear as “via Windows Phone (via Windows Live)” for the Twitter source application. Clicking on the link will redirect you to Microsoft’s Windows Phone site. Previously builds of Mango said “via Windows Phone(via Windows Live)INT.”

Microsoft is in the final stages of Mango and will likely release the final build to devices during September or October. The software giant hinted at a release date by promising Imagine Cup 2011 contestants Windows Phone 7.5 (Mango) devices “by September.”

Image Credit: WPCentral