Mobile OS Revolution: Android 4, Windows Phone 7.5, and Apple iOS 5 Explained
Windows Phone 7.5 (Mango)
Windows Phone is the newest member of this group, and as such had the most room for growth. Microsoft’s Mango update to WP7 launched simultaneously to multiple devices on carriers throughout the world, and did so without any major hiccups. The update will be available to all Windows Phone devices and will become stock on a new wave of hardware arriving in the coming months.

General
The biggest update in Windows Phone 7.5 is Multitasking. Like iOS, most Windows Phone apps don’t truly run in the background, but Windows Phone 7.5 provides the APIs that developers need to do critical things, like play music or continue downloading files while the application is inactive. You can switch between running applications by holding the back button, swiping through the available options, and tapping on the app you want.

Messaging and Social Networks
Microsoft’s tagline for Windows Phone is “Put People First”, and Mango improves on that goal in dramatic ways. Already one of the more socially connected platforms with Facebook integrated directly into the OS, WP7.5 also includes Twitter and LinkedIn integration, as well as improving the Facebook support. The “Me” tile can update any of the connected social networks, and you can follow friends through the People hub. Also through the People hub, the new History pivot tracks your interaction with individual friends, both via the integrated social networks and the more traditional means.
The Messaging app in Windows Phone is where you would typically read and send SMS and MMS messages. The Messaging interface itself received some minor tweaks, a rarity in this update, with incoming and outgoing messages being colored differently. The Messaging app is also the home of integrated Facebook chat. Messaging allows you to seamlessly switch back and forth between Facebook chat and SMS, much like Facebook Messages. Voice integration is another new feature of the Messaging app, allowing you to easily dictate text messages using only voice commands.
Windows Phone 7 included one of our favorite mobile email implementations before Mango, and it only gets better. Email in Mango has a threaded view, making it simple to view an entire conversation without searching through your email history. Also new in Mango is the ability to link inboxes. Linked inboxes let you associate two or more email accounts to handle as one, simplifying the task of managing your email without losing the benefits gained by having multiple accounts.
Bing
When the search button gets one of the three mandated hardware buttons on every Windows Phone device, there’s a good chance that Microsoft has big plans for Bing in Windows Phone 7. We’ve already covered much of Bing’s new functionality in our piece on Tips and Tricks for Mango, but know that if you aren’t using Bing on a regular basis, you’re missing out. Scout, Music, Vision, and Voice all have new features and use cases that have major potential, and compete favorably against the best Apple and Google can offer.

Other
There are too many new features in Mango to fully delve into here, but some other items of interest include support for custom ringtones, new features in Zune (Music and Video), and the ability to save Office documents to SkyDrive. Mango also offers many new capabilities for developers that you'll see in your apps, such as the ability to pin multiple live tiles to your Start screen.
Let's Get Moving
Regardless of which mobile platform you use on a daily basis, there are some good reasons to be excited about the new things on offer. Each platform has made major steps forward in features and how the UI presents those features.
The real question for many people is if their device will be supported, and unfortunately that often depends on the device. Most Apple devices are eligible for iOS 5, but will miss out on the most innovative feature in Siri. All Windows Phone devices are upgradeable to Mango, partially due to the small segment of the market held by Windows Phone. The upgradeability of Android devices is an entirely new conversation. The general rule of thumb says that popular devices from Google partners released in the last 18 months have the best chance for an upgrade, but the schedule for those devices to receive their update is anyone’s guess.
Which is your platform of choice? What new features are you looking forward to the most? Let us know in the comments!