Microsoft first talked about Windows Phone 8 back in June at the Windows Phone Summit, where it detailed the 8 major new features coming to the next version of the mobile operating system. Samsung, Nokia and HTC have each unveiled their preliminary lineup of WP8 devices during the past couple of months.

Yesterday Microsoft officially launched Windows Phone 8 worldwide at an event in San Francisco and also showed off some previously unannounced features (although information about some of them had leaked a while ago). Aside from those revealed at the WP Summit, these are the biggest new features coming to WP8:

• Data Sense

  This amazing new feature gives you great control over your data plan. To start with, when you browse the Web, the Data Sense technology automatically compresses all images on the cloud before downloading them to your phone, letting you browse up to 45% more Web pages on the same data plan. It helps you find Wi-Fi hotspots when you're on-the-go and intelligently defers data-intensive tasks to when Wi-Fi is available. Data Sense also shows your data usage on a per-app basis and even notifies you when you get close to the plan limit.

• Rooms

  Rooms let you create groups of contacts within the People Hub. You can then send private messages and share notes, calendars, pictures etc. privately with the members of the Room. A Family Room will be present by default on all phones. Some parts of the Rooms feature, such as sharing calendars, will also be available to iPhone users who are part of a Room.

• Kid's Corner

  Kid's Corner is intended to keep kids from using parts of the phone that their parents don't want them to use. It allows parents to whitelist the apps, games, videos and music their children can have access to. This means problems like kids sending accidental texts or making unasked for purchases should be a thing of the past. Kid's Corner is activated simply by swiping left on the Lock Screen, and also has a Start Screen of its own. Model and actress Jessica Alba came on stage to talk about how she uses Kid's Corner.

• New apps

  Microsoft said that the count of apps in the Windows Phone Store has crossed the 120,000 mark and that 46 of the top 50 apps on other smartphone platforms will become available on Windows Phone shortly. One of those apps, arriving early 2013, is the popular Internet radio service Pandora. Microsoft will sponsor one full year of music free of cost and free of ads. The new and improved Skype app will be "always on", so you can receive Skype calls at any time, and making and taking Skype calls will work exactly like a regular phone call.

• Live Apps

  Basically, any app that can have its own Live Tile on the Start Screen is now called a Live App. But here's what's new: In Windows Phone 8, a Live App can also deliver real-time information straight to the Lock Screen. For example, you can have Bing automatically update your Lock Screen wallpaper to the day's Bing home page image.

CEO Steve Ballmer later shared details about availability and pricing of the new phones. The five Windows Phone 8 devices announced so far - Nokia's Lumia 920 and 820, HTC's 8X and 8S, and Samsung's ATIV S - will go on sale in November. Different variants of these phones will be available on AT&T, Verizon and T-Mobile in the US.

Image credit: Microsoft News Center (modified)