Microsoft began rolling out its updated Windows 7.5 Mango OS this morning for download but only to select smartphone users.

Existing Microsoft Windows Phone users can begin downloading the "Mango" update but which users are eligible to download the update is still unknown.

"We plan to begin delivering the Windows Phone 7.5 update to a small percentage of existing customers on Tuesday Sept 27th," Microsoft said yesterday in a statement.

"We'll gradually ramp up delivery so that the update will be broadly available to most existing Windows Phone customers by the end of October. "

Microsoft has set up a helpful "Where's My Phone Update?" website so users can be notified when their updates come. However, going to the website will only tell users to be patient and wait for the updates on their phone.

The wait for the Mango is worth it given the new features the OS will be getting. With the Windows 7.5 users can customize their home-screen tiles to activate shortcuts for apps. Users can also use the tiles to alternate between text and visual themes.

Another new feature in the update is the ability to use the new groups' hub to select and merge content from various social networks like Facebook, Twitter, LinkedIn and Microsoft Exchange.

Mango will also allow users to merge feeds from their contacts and then merging all the information they gathered from different social media platforms into feeds. The Mango update will also introduce the idea of smart agents or apps that can get information even if they run in the background. For example one app from Qantas will automatically remind a user if they are running late for a flight.

Microsoft will also launch a web-based Marketplace for its apps. Currently there are 30,000 apps for users to choose from and Microsoft will allow third-party apps for Mango.

Microsoft will bundle a full version of Office Mobile with the Mango as well as an IE-9 based browser that supports HTML-5 and hardware acceleration.