Windows Phone 7 is shipped on devices that meet Microsoft’s design guidelines. Microsoft enforces specific requirements around the types and locations of buttons and logos, and there are rules requiring the single screen resolution supported by Windows Phone 7.

The user interface of WP7 is different. Rather than icons, WP7 uses start page with tiles that can indicate status like the number of emails, facebook notifications etc with easy access to launching the application. Once launched from tiles or the list of applications, non-game applications appear quite visibly different from other platforms in their design, which uses side scrolling design metaphor intended to organize information into unique views or tasks on individual pages.

Similar to iOS, Microsoft approves applications before they can be downloaded. WP7 does not support multi tasking. It also offers limited user customization options.

Reference: Redmond mag