By now, HTC's sold well over 2 million units of its Touch Windows Mobile-run smartphone. At CTIA this week, we got a chance to check out the latest edition of that device, the Touch Dual, headed to the U.S.

Unlike the original all-touch-screen Touch models, the Dual Touch sports a 20-key keyboard that slides out from underneath the display. The idea is to make it easier to input text for working on documents as well as sending SMS and e-mail messages.

Of course, being a HTC Touch and all, the Touch Dual will also feature HTC's proprietary TouchFLO interface, which runs on top of Windows Mobile and allows for finger-touch scrolling, panning and photo zooming, for example.

The Touch Dual, a quad-band GSM world phone with support for 3.5G data transfers, won't be available directly from any carriers when it ships. Rather, HTC will sell it unlocked through Best Buy and its own retail site, for an as-of-yet undisclosed price.

That means if your a customer of a GSM carrier like AT&T (the only American operator with support for GSM-style 3G and 3.5G) and T-Mobile, all you'll need to do to use the Touch Dual is pop in your SIM card.

  
Pictures of Touch Dual on the CTIA show floor.

Additional features include a 2 megapixel camera for photos and videos and a second camera for video calling. It's got 128MB of RAM, a microSD slot for storage expansion, and a 400MHz processor.

There's no Wi-Fi, though, which may not be that big of a issue with 3.5G support.

Significantly, the Touch Dual will be one of the first devices run Microsoft's just announced upgrade to Windows Mobile upgrade, version 6.1, which provides new timesaving features, easier phone navigation and management, stronger security safeguards, and support for Microsoft System Center Mobile Device Manager 2008.

HTC says the Touch by HTC and Mogul by HTC from Sprint, AT&T Tilt, Alltel Wireless’ HTC Touch and PPC6800, and the HTC TyTN II be among the first of its many devices that'll get Windows Mobile 6.1 upgrades.