It's almost sure that Microsoft will reveal Windows Phone 7 at Mobile World Congress on February 15.
Some of the details for Windows Phone 7 have leaked out. One of the main concern is that will not support multi-tasking. Also it lack flash support due to time constraints and backward compatibility.
The latest leaks suggest that:
The browser will be based on IE7 codebase but will include some IE8 functionality.
Windows Phone will be more like the Zune HD.
App installation is from the Marketplace only, not from SD storage card.
OEM Interfaces will not be allowed to run on the device.
XBOX Gaming Integration
Support for social networking
The First Windows Mobile 7 devices are expected to ship in September of 2010 according to the rumors ... but we'll know on 15th of February.