We have known for some time that Tango, the codename of a Windows Phone build that is set to land between Mango and Apollo (Windows Phone 8), is real. However, until now, we have had scant hard evidence of it outside of the occasional leak and rumor.
No more. Today, it has been uncovered that a new build of Windows Phone is out and about, and many are labeling it as potentially being the elusive Tango edition of the WP7 firmware. The current, stable build of Windows Phone is number 7740, while the new build is 8713 (technically 7.10.8713).
Tango is believed to contain a number of feature upgrades, including NFC and LTE support, and also the ability to run on lesser hardware, allowing for Windows Phone handsets to sell at increasingly low price points. Another rumor has the update as only being available to Nokia. However, the handset caught running the 8713 build of Windows Phone was an HTC handset, for what it is worth.
For now, we can assuredly say the following: Development of the Windows Phone platform has not slowed. With Mango coming out early, and with this build arriving as it has, it could be that Tango will be released before we expected it to. I would be loath to say that this could indicate that Apollo, Windows Phone 8, might also be potentially ahead of schedule, but that is not outside the realm of possibility. At this time, things appear positive, but much could change before either update is ready for general release.