Hidden in a Nokia press release for the Lumia 610 you come to the information of when the Windows Phone “Tango” update will be hitting other Windows Phone devices. According to them, the update will be available sometime in April and will still come under the “Windows Phone 7.5” version umbrella.
It seems to indicate the update will be available for devices that are not low-end, with the major selling point being improved support for China in both language (via software) and networks (via hardware). Other things that the Tango update will bring include lowering the hardware requirements to support 256 MB of RAM and Qualcomm’s MSM7X27A S1 Snapdragon processors that can be clocked as low as 800 MHz as we can see in the Lumia 610.
As you might expect from lowering the hardware requirements, there are some downsides on the software side. Bing Local Scout is not available for these devices, and automatic photo uploads to SkyDrive is not supported (although manual uploads are still possible). Some Marketplace applications, and more likely games, will also probably not be supported on the slower hardware.
Now it isn’t entirely clear as to whether the Tango update will be available to consumers in April or simply hardware manufacturers. The Verge indicates that the latter is what will occur, although as manufactures such as ZTE and Nokia clearly have the update already there is a possibility that we’ll see it on already released devices in April. There aren't many announced updates that cater for higher-end devices though, so it mainly helps hardware developers create cheaper WP hardware.
Also out now for all the Windows Phone developers out there is a test SDK update, which includes a new Windows Phone emulator that allows you to test apps on 256 MB of RAM in preparation for Tango. As it notes clearly on the download page, it’s a pre-release update with no support for publishing applications. Microsoft also advises against installing it on your primary development machine.