Microsoft's latest Windows Phone OS, code-named Mango, is set to launch this fall, which is around the same time Apple Inc.'s iOS 5 comes. But can Mango be sweeter than Apple iOS 5?

Mango (or Windows Phone 7.5) is expected to give the much-needed boost to Microsoft, whose performance has "gone from very small to....very small," Chief Executive Steve Ballmer said.

Microsoft has officially signed off on the release to manufacturing build of Mango, which marks "the point in the development process where we hand code to our handset and mobile operator partners to optimize Mango for their specific phone and network configurations," according to the Microsoft blog.

"The Mango update for current Windows Phone handsets will be ready this fall, and of course will come pre-installed on new Windows Phones," the blog read. Microsoft had confirmed Acer, Fujitsu and ZTE Corp. as key original equipment manufacturer (OEM) partners to manufacture Mango devices.

The first phone to grace the updated Windows Phone 7.5, or Mango update, is Windows Phone ISI12T, manufactured by Fujitsu Toshiba Mobile Communications, which will be launched in September.

Since May, Mango has been making a buzz when Microsoft showcased its newest mobile OS. It has hundreds of new features, including:

New email Conversation View: It the user to efficiently participate in long email discussions with friends and co-workers.

Threads: It combines the user's text, IM, and Facebook chat all into one conversation.

True Multitasking: Mango is the first mobile OS from Microsoft to offer true application multitasking.

Powerful Search Function: Mango connects apps to search results and deepens integration within the Hubs like Music and Video and Pictures.

Internet Explorer 9: Mango includes IE9 for faster web browsing and support for new HTML 5 web sites.

Cloud: Mango has been designed to integrate native phone functions with Microsoft's cloud offerings like Xbox Live, Microsoft Office 365 and SkyDrive services

However, in terms of features, Mango is sour compared to iOS 5, whose buzz is getting louder ever since Apple gave a sneak peek in June during its annual Worldwide Developers Conference (WWDC).

Apple said iOS 5, the latest version of its mobile OS, was a "major" and "incredible" release for developers and customers alike and the iOS 5 comes with 1500 new APIs and 200 new features, including:

iMessage: iOS users can send unlimited text message through iMessage, as well as other multimedia messages over Wi-Fi and 3G. It allows you to get read and delivery receipts and real time typing indication. The iMessages can be pushed out to all iOS devices a user owns, thereby allowing, for instance, the user to start a conversation in iPhone and continue the same on an iPad right where it was left off.

Reminders: With the look of white loose-leaf paper, the built-in Reminders app in iOS 5 helps the user to manage multiple to-do lists. The reminders will be alerted based on due dates and also locations. The most attractive element probably is that the Reminders can work via iCloud, which means it can alert you on multiple Apple devices in real time. Mac users and PC users can also expect Reminders to sync with iCal or outlook when iOS 5 finally comes out.

Notifications: A new, convenient notification system in iOS 5 was introduced which combine all notifications in one place. The Notification Center can be accessed by swiping down from the status bar at the top of the screen. Apple said the new push notifications have been “scaled beautifully” and are no longer annoying or obtrusive. The notifications will be displayed on the lock screen together with stock and weather alerts. Now, when a notification appears in a lock screen, tapping the notification will automatically open the related app. The UI also looks radically cool thanks to nifty animation effects.

FaceTime: FaceTime is one of the  advanced features that Apple users love. iOS 5 will allow users to access FaceTime over WiFi. You can also set it in motion with your email as ID if the activation with phone number fails. However, there are rumors that FaceTime over 3G has also been enabled in iOS 5.

Camera: With the new feature of camera in iOS 5, users can capture the precious moments immediately by accessing the camera using a shortcut on lock screen. To take a photo, just double tap the home button and then tap the camera icon. And then simply tap the volume up button to capture. New Camera also makes it possible for users to use crop and rotate, edit, red eye reduction, auto focus and auto exposure, and auto enhance (using iPhoto) function.

PC Free: Apple's iOS 5 is “PC free”, which means iOS updates are now possible over the air. There is no need to hook up mobile Apple devices with PC to access iTunes. As long as Wi-Fi is available, iTunes sync is now automatic and possible even while an iOS device is being charged. Also back-up and restoring can be done automatically via iCloud.

Mobile Safari: The new mobile web browser now has several new features including tabbed browsing (switching between tabs is “lighting fast”) and the Safari reader feature that allows the users to quickly save stories for later reading in the Reading List. The Reading List can be synced across multiple devices.

The Mobile Safari also enables users to email story content together with link and if the user so desires. The Safari Reader will get rid of reviews, ads and other unnecessary content on the page to enable user to dive right into essential stuff.

Twitter Integration: Apple has integrated Twitter into iOS to make it easier to tweet from iPhone. There will be a single sign-in for Twitter and all related apps. Twitter UI has been integrated with the camera as well as Photos and Maps and Safari. Contacts have also been integrated with Twitter.

Delta updates: Delta updates will be available on iOS 5 i.e. software updates are now over the air and you can download only the necessary update and not the entire app/software.

Better Accessibility Settings for Those with Disabilities: Apple has enhanced the accessibility setting for users with physical disability on iOS 5. iOS 5 now support special hardware for people with visual, auditory, tactile, or cognitive disabilities. As the LED camera flash now works with a custom vibration setting, you can actually see and feel when someone is calling. Moreover, you can also set custom vibration patterns, so that you can easily identify the caller and make out the difference between a call, an email, and a text without even looking at the phone.

As Microsoft is gearing for the Mango devices launch, it has key challenges ahead in addition to Apple iOS 5 as Google Inc. is also expected to launch the next version of its Android OS, Ice Cream Sandwich, with Nexus 4G by Thanksgiving. Thus it will face both Android and iOS 5 phones that already have a head start.