File this under rumor, folks, as these screenshots can easily be faked, but PocketPC.ch is reporting that Windows Phone "Tango" will be known as Windows Phone 7.6 and has the build number starting at 7.20.1050.5. More importantly, they allege that it will include Google+ in addition to Skype. Via Bing Translator:
"In this early beta phase, the implementation of Skype and G + is still rather experimental. Telephoning via Skype seems to work not as yet, but it is prepared. G + chat and Skype chat work but already well. The front camera, which will be the next generation of Windows phones standard, is included in the Skype video calling. It is thus possible to receive video calls and to make, but in the pre beta with some problems and crashes. That Google Hangout, the video calling G +, will also follow, is likely, but the timing is still unclear, given that the API of G + is still not so far advanced, to make this possible."
In other words, the reason we have not yet seen an app for Windows Phone is because Microsoft has evidently pushed up the integration from Apollo (Windows Phone 8) to Tango (Windows Phone 7.6), making this update much more significant. In addition, Microsoft is also evidently pushing out Google+ into the mix which makes sense from a "cover the market" perspective, but should be surprising to many including those on Android, assuming it is true.
Hopefully we'll find out more in the coming weeks as to the validity of this leaked image and the content therein. But if accurate, "Tango" looks to be quite major, indeed.
Edit: As pointed out in comments by J45PER, the font for the o's in "Google" look and are spaced differently than "Facebook", calling into question the validity of the image. However, it's not clear if PocketPC.ch is claiming the screenshot is real or were just using it for illustrative purposes.
Edit 2: The source, PocketPC.ch, is denying that they faked the story or image. We of course have doubts like you, but we'll find out soon enough. Link to the "new" watermarked image, for what it's worth.
Source: PocketPC.ch; Thanks, Benjamin, for the tip!