The NumberOfSoftkeys property applies only to WML-compatible mobile devices.
Soft keys are special keys that the application can usually map to custom tasks. Soft-key text is displayed on the screen in the lower-left and lower-right corners.
Windows 98, Windows Server 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.