Verizon Wireless customers choice of smartphones is about to go up considerably. The country's second largest mobile operator is now shipping the Samsung i760, a long-awaited Windows Mobile slider with both a QWERTY thumb-keyboard and a numeric keypad. It also has two additional Microsoft-based devices, the XV6800 and SMT5800, and the Treo 755p on tap.

With the i760 the keypad is on top so it’s accessible when the Windows Mobile 6 Professional device is closed. You access the full keyboard by sliding the smartphone open horizontally.

The i760's 240 x 320 pixel (QVGA) resolution touch screen measures 2.8 inches diagonally, while the device itself measures 4.5 x 2.3 x 0.77 inches when closed. It weighs 5.3 ounces.

There's a 1.3 megapixel camera with a flash for picture and video, Wi-Fi, Bluetooth 2.0, 128 MB of ROM, 64 MB of RAM, and a microSD slot for storage expansion.

The i760 supports Verizon's 3G EV-DO network for fast data transfers when Wi-Fi isn't present.

Verizon lists the i760 for $300 with a two-year contract and after a $100 on-line discount.

As for the other two Windows Mobile smartphones on Verizon's agenda, both the XV6800 and SMT5800 sport a 2 megapixel camera and Bluetooth.

The former is based on HTC's Titan design and is designed to go up against powerful horizontal sliders with full keyboard models like Sprint's Mogul or AT&T's Tilt. Like the Samsung, the XV6800 is a Windows Mobile 6 Professional device. So it’s got a touch screen.

As for the SMT5800, while it is also HTC-built, it runs on the Standard version of Windows Mobile 6, which means, among other things, no touch screen. The SMT5800 is a candy bar-style phone with a numeric keypad. It’s far less powerful than the smartphone models listed in the preceding paragraph.

We'll let you know more about these two smartphones, including price, as they get closer to release.

A lot is already known about the Treo 755p, of course, as it’s been out for half a year already. The replacement for the Treo 700p was first picked up by Sprint, followed by Alltel, which announced it was carrying the smartphone earlier this week. That puts Verizon at the distinct disadvantage of being the third carrier in the U.S. to pick up what could be Palm's last Palm OS Treo.

Like with the XV6800 and SMT580, Verizon did not say when it would ship the 755p. The only thing we know for sure right now is it’s supposed to be in time for the holiday season.