It's a fairly open secret (since a December FCC leak) that Asus is all set to be the fifth manufacturer to join Microsoft's mobile revolution - with the Windows Phone 7 touting Asus E600.

But this is the first time we've seen video action of the handset all booted up and ready to go.

The E600 is said to be packing a 4ish-inch display, along with a 5-megapixel camera with LED flash. Other specs confirmed by the FCC listing include a 1300mAh battery, micro-USB port, lock/power button and a 3.5mm headphone jack. 

Vietnamese site (what is it with Vietnam and phone leaks?) Tinhte grabbed the video along with some new pics of the WP7 device.

We expect to see it officially unveiled over in Barcelona next month at Mobile World Congress.