Just a few weeks before it officially hits, Windows Phone 7.5 Refresh aka "Tango" (build 8773) has managed to be dumped onto XDA for the world to see (and use). Wasting no time, some chefs have already cooked up some custom ROMs for the HD2 (which will evidently live until the year 2031 with updates) and the Samsung Omnia7.
More ROMs will be expected to follow soon for first generation devices, notably HTC ones and the Samsung Focus. Since there are no custom ROMs for Gen 2 devices (due to a locked bootloader), we're not expecting this Tango ROM to help too much though perhaps some folks at XDA will find a way.
Tango is thought to a "refresh" of Windows Phone 7.5 with only minor, under the hood changes including support for lower-spec'd devices (256MB of RAM) as well as some MMS improvements and a fix for the SMS bug. Like all previous updates, this is expected to trickle out for current phones but only at the discretion of the carrier.