According to Windows Phone Italy, which had the chance to sit together with Stefania Duico, the head of Windows Phone for Microsoft Italy, Microsoft plans to call its upcoming Tango update "Windows Phone 7.5 Refresh". If you remember, the initial release was called Windows Phone 7 which became Windows Phone 7.5 with last fall's Mango update. The expected "Refresh" name stands in a long history of weird mobile product names (maybe the most weirdest one was "Windows Mobile 2003 Second Edition" which was available for "Pocket PC", "Pocket PC Phone Edition" and "Smartphone". Thankfully "Windows Phone 7.5 Refresh" sounds much nicer than "Windows Phone 7.5 Second Edition".
Unlike the previous Mango upgrade, the Tango update is expected to be a minor release on the way to Windows Phone 8, which is expected to be Windows Phone Apollo (more on this topic soon). However, Microsoft has yet not unveiled a release date of Tango, while it's expected that Windows Phone Apollo will be launched anytime end of this year.
Cheers ~ Arne