NaviFirm is the ultimate place to get info about upcoming firmware updates for Nokia phones. It has now given clue about Windows phone’s new firmware update which is claimed to be Tango version and brings many new features to the Lumia range of Phones and support for windows phones with lower specs.
Versions 1600.3030.8773.12120 is available for both 710 and 800C, the chinese CDMA version of Lumia 800 .The other version 1600.3029.8773.12111 is specific to Lumia 710 for now and seems to be available for Chinese Lumia devices only.
Check the screenshots below,
