A senior member of XDA forums has just leaked an unofficial Windows Phone 7.5 "Tango" ROM, nearly one week before it launches. This build (v126.96.36.19973) can be converted into a properly-working custom ROM and then installed on handsets that currently run Windows Phone 7.5 Mango.
Developers have already started tweaking this build and now owners of the HTC HD2 and Samsung Omnia 7 are now able to install it. The update can be also previewed on the newly-released HTC Titan (known as Triumph in China) which comes preloaded with Tango.
WP 7.5 Tango is set to launch on March 21st, when Microsoft will hold a presentation event in Beijing. The last major Windows Phone Tango update was build v7.10.7720 and then received two small upgrades, 7.10.7740 and 7.10.8107, which fixed notification issues and added LTE support.
Tango will bring minor improvements like SIM management options, enhanced MMS support, new roaming settings, support for low budget handsets which come with 256MB of RAM or less, and also, adding a notification icon showing whenever the phone shares location settings.
Source : XDA Developers