Windows Phone 7's graphical user interface is based on the "Metro" style Microsoft originally designed for the Zune MP3 player. The OS eschews the app icons familiar to iOS and Android users for brightly colored square and rectangular tiles, some of which receive live updates to display new information like recent text messages or the current weather forecast. The colored tiles and strict hardware requirements promote the same goal: a consistent style across devices.
Since Windows Phone 7's launch in late 2010, Microsoft has updated the operating system to include a variety of features, including copy and paste, multitasking, more live tiles, threaded messaging, and custom ringtones. This is the version of Windows Phone 7 that ships on the Lumia 900 -- Microsoft calls it Windows Phone 7.5. Windows Phone 7 will become Windows Phone 8 when Microsoft releases the next major update for the platform; it's expected to happen around the launch of the Windows 8 desktop operating system at the end of 2012 [source: WinSupersite].
The Windows Phone platform lags behind iOS and Android in available apps on its marketplace, but it's younger than both of those competitors and passed the 50,000 app mark in late 2011 [source: PCMag]. Windows Phone 7's app market includes official apps for popular services like Facebook, Twitter, YouTube, Netflix and Kindle. Microsoft also offers apps for its services like SkyDrive, Office and Skype, which the company purchased in 2011.
Those apps are productive staples of any mobile ecosystem, but Microsoft pushed a very different focus when it launched Windows Phone 7: fun. Thanks to the Xbox Live brand, Windows Phone is brimming with games -- some of which were originally published on the Xbox 360's Xbox Live Arcade. While Apple's iOS still has the strongest library of games, some of its most popular titles like "Angry Birds" and "Fruit Ninja" are available on Windows Phone, and Microsoft offers a number of exclusives through Xbox Live.
Nokia's Lumia 900 will run those games and apps like any other Windows Phone, but Nokia includes a little of its own software on the side. The phone's predecessor, the Lumia 800, shipped with Nokia Maps and Nokia Music pre-installed. The former provides offline turn-by-turn navigation based on map data, while the latter includes a free music streaming service called Mix Radio [source: TheVerge]. While the included apps could vary by region, Nokia will also offer Nokia Reading on the Lumia 900, an app that promises to bring all your digital written media together for easy access both on- and offline.