Shortly after Microsoft rolled out Windows Mobile 6.1 at last week's CTIA Wireless show in Las Vegas, Sony Ericsson announced its first Microsoft-run smartphone, the Xperia X1, would ship with the platform upgrade installed. The X1 is major change of pace for the cell phone company, as it usually builds smartphones on the Symbian OS and its own UIQ platform.

One of the most anticipated Microsoft-run smartphones in some time, the X1 is supposed to ship during the second half of this year, but may, according to rumor, be delayed until early 2009. It sports a unique arc slider design, so when you slide up its high-resolution 3-inch, WVGA (840 x 480-pixel) touch screen, a wide QWERTY thumb-keyboard is revealed.

Windows Mobile 6.1 includes a number of enhancements over 6.0, particularly regarding the user experience but also under the hood. Improvements include new time-saving features, such as one-tap Bluetooth and Wi-Fi access, easier phone navigation and management, increased security safeguards, threaded SMS, and a new look to the today screen.

Microsoft also plans to make an upgrade to Internet Explorer Mobile that promises "desktop-grade" browsing to its handset partners in the third-quarter. There's been no indication whether or not the X1 will feature this browser update when it shops or if it'll be made available for download afterward.

At CTIA, we got a chance to play with the X1. In our limited time with the smartphone, we found it to be solid and well designed, with a keyboard that’s comfortable to type on.

Like HTC with the Touch and some other smartphone vendors, Sony Ericsson is grafting a proprietary user interface on top of Windows Mobile, to enhance usability. And, like the Touch, Sony Ericsson is using its customer interface as an opportunity to bring some iPhone-like functionality to the X1's touch display.

Below are a few pictures we took of the X1 during our short hands-on with the smartphone.

As a quad-band GSM phone, you'll be able to use the smartphone to make voice calls in most world markets. It supports 3G cellular-wireless data networking in many countries as well.

There's also Wi-Fi, Bluetooth, A-GPS for location-based services, FM receiver and 3.2 megapixel camera for picture and video.

A microSD slot is available to compliment the X1's 400MB of internal memory with gigabytes of additional storage.

The smartphone measures 4.3 x 2.1 x 0.66 inches (110 x 53 x 16.7 millimeters) and weighs in at 5.1 ounces (145 grams).

Sony Ericsson is giving operators a chance to build custom touch panels for the that run on the X1 through its touch interface, thereby giving users better access to each operator's specific set of applications and services.

See next page for a comprehensive list of the X1's specifications.