The Windows Phone "Tango" upgrade has been pre-installed on a number of devices, including the Nokia Lumia 610 and the European version of the Lumia 900. However, the Tango update has yet to be released for existing Windows Phone devices. Now Microsoft has updated its Windows Phone update history page that lists what's new in the Tango version.
The update has the official build number of 7.10.8773.98. The page gives some information on what's included with this new upgrade. In terms of messaging, the Tango version allows users to "attach multiple pictures, videos, audio notes and ringtones to text messages". The Tango build also lets Windows Phone owners "export phone contacts to a SIM card and selectively import SIM card contacts to your phone."
Finally, the page says that Tango adds "many other improvements to Windows Phone." Yep, that's about as vague of a description as you might get, but there it is.
Again, while the Tango version of Windows Phone is pre-installed on a few new Windows Phone devices, there's no word from Microsoft or any of the wireless carriers that sell Windows Phone products when it will be made available to download for all those existing devices currently on the market.