The details about Microsoft’s new operating system Windows Phone 7 Series – which apparently will be different from Windows Mobile in look and feel, and will support applications sold via the Marketplace – have started making rounds, via official as well as unofficial channels.

Going by the leaks about the Windows Phone, the application development for the OS will use almost all managed code. App developers will be offered two frameworks – Silverlight and XNA. While the former is a cross-platform .NET environment being touted as an Adobe Flash and Adobe AIR challenger; the latter is Microsoft’s gaming platform in use by hobbyist developers for the Xbox 360 console.

Designed to make use of the forthcoming Visual Studio 2010 development environment, and Expression Blend design tool, Windows Phone development – wherein Microsoft expects the developers to leverage its ever-increasing stable of cloud services – will require connectivity of the apps to data sources.

The basic principle behind Windows Phone app development will be “3 Screens + the Cloud;” with the phone, the PC, and the TV being the equally-important three ‘screens,’ on which relevant information will be tied together.

With the leaks also revealing that the Windows Phone OS supports full preemptive multitasking of multithreaded applications, Microsoft itself claims that the Windows Phone 7 Series development will be “very compelling” experience; thereby offering “the best development platform in our history.”