AT&T has announced three new Windows Phone 7.5 Mango devices will be joining their smartphone lineup this fall. The company also plans to make Mango available to all Windows Phone customers later this year.

The HTC Titan will debut with the largest screen in AT&T's portfolio at 4.7-inches. The smartphone features a 1.5 GHz processor and an 8MP rear camera with dual LED flash. Engadget got their hands on the Titan last week and found 512MB of RAM and 16GB of flash storage onboard.

Two Samsung smartphones are also joining the Mango lineup. The first is the Focus S, the successor to the original Focus which holds the title as the highest selling Windows Phone in the US. The revision features a 4.3-inch Super AMOLED Plus display, a 1.4 GHz processor, an 8MP rear camera and a 1.3MP front facing shooter.

The budget-minded Focus Flash includes a smaller 3.7-inch Super AMOLED screen, a 1.4 GHz processor, a 5MP rear camera and an unspecified front facing lens.

These phones will be joining the HTC HD7S, HTC Surround, LG Quantum and Samsung Focus to round out the company's Windows Phone lineup.

Windows Phone 7.5 Mango update adds a number of much-awaited features, including an HTML5 version of Internet Explorer 9 for mobiles, deep Twitter integration, better multitasking support, an improved messaging system, new Bing features and so on.

This could very well be Microsoft's last real opportunity to steal a piece of the pie from Google and Apple. A comScore report from August showed that Microsoft ranked fourth in smartphone market share behind Google, Apple and RIM in that order.