T-Mobile and HTC today announced a new version of the T-Mobile Shadow, a popular low-end Windows Mobile smartphone. The new Shadow has a faster processor and supports unlimited calls over Wi-Fi hotspots, as well as calling over regular cell-phone networks.

The new Shadow—T-Mobile changed the product but not the name, annoyingly—has several improvements over the old model. Both phones are sliding, non-touchscreen Windows Mobile phones with an unusual hybrid keyboard, much like the BlackBerry Pearl’s. The keyboard puts two letters on each key, making it easier to type on than a standard phone keypad, but not as physically wide as a full QWERTY keyboard.

The new Shadow has a faster processor than the old one, 260 Mhz compared to 201 Mhz. That’s still a slow processor to run Windows Mobile—we prefer 400 Mhz or greater—but this is intended to be an inexpensive phone. It runs Windows Mobile 6.1, as opposed to the older model’s 6.0. And while both phones had EDGE and Wi-Fi for connecting to the Internet, the new Shadow supports T-Mobile’s Unlimited HotSpot Calling (formerly known as Hotspot@Home), which lets you make unlimited calls over Wi-Fi networks anywhere in the world for $10/month.

Like all Windows Mobile phones, the Shadow syncs very easily with Windows PCs and connects quickly to both POP3 and Microsoft Exchange e-mail accounts, instantly updating e-mail, calendar and contact information stored on Exchange servers. The Shadow also comes with a multi-platform IM program.

The new Shadow has a slightly rounder body than the older model, and comes in striking black and white colors. The phone is 4.06″ x 2.05″ x .59″ and 5.29 ounces. It has a 2.6″, 320×240 TFT LCD screen. There’s a 2-megapixel camera with video capability on the back. The phone can use MicroSD memory cards up to 8 GB, and has stereo Bluetooth support.

T-Mobile didn’t announce a price for the Shadow, but the previous Shadow was an affordable phone, often seen for $149 or even $99 with discounts. The new model will be available within the next few weeks, T-Mobile said.