Sources close to the matter claim that the upcoming Windows Phone 7.5 update, known as Tango, will be served to most handsets starting around the beginning of June. The build should arrive to SIM-free versions, prior to carrier branded phones.
Although the ROM is finalised and can be currently found on Nokia's Lumia 900 and the HTC Titan II, it seems that Microsoft has chosen to delay the roll-out in favour of a more universal updating process. This happened mainly because most carriers haven't finished testing the latest 8773 build.
Sources also state that Microsoft wants all operators to serve the update in a limited time interval, so as to prevent any potential huge delays. The serving process is also expected to be as wide as in the case of Mango, a major version that runs on over 85 per cent of handsets taking almost two months to complete.
Tango, previously known as Refresh, is the latest Windows Phone update to arrive on the market, along with the arrival of the HTC Titan II. This build will be optimised for lower-tier handsets (those with less than 256MB of RAM), allowing them to run demanding applications with limited options.
The version will also bring enhanced MMS support, new settings for roaming and SIM management, while adding a new range of privacy alerts that focus on tracking location-related data.
Source: Mi Movil Windows (translated by Google)