It has been perhaps Palm’s worst kept secret, long rumored as the ‘Treo 850′ with leaks posted on many sites, but Palm has finally officially announced the Palm Treo Pro. The Treo Pro is the latest in Palm’s Treo product line, though it looks more like a next-generation Centro than past Treo models. But while the Centro is an inexpensive entry-level smartphone running Palm OS, the Treo Pro is a high-end smartphone running Windows Mobile Professional 6.1.

The Treo Pro is fully tricked out with a 400MHz CPU, 256MB memory (100MB user accessable), 128MB RAM, 802.11B.g WiFi, 3G cellular support with HSDPA/UMTS/EDGE/GPRS/GSM (tri-band UMTS, quad-bad GSM), GPS, a 320×320 touchscreen, Bluetooth 2.0+EDR, microSDHC card support, a 3.5mm headphone jack (aka a standard jack, not the tiny 2.5mm jack on many phones that requires an adapter), and a 2.0 megapixel camera. And Palm has done their usual job of enhancing the WinMob interface to make it much more usable.

Since it is a GSM world phone it should work on pretty much any GSM-based carrier, such as AT&T or T-Mobile, but it won’t work on CDMA carriers like Verizon or Sprint. Palm is also touting the ability to use the Treo Pro as a high-speed cellular modem for your laptop, aka tethering, over USB or Bluetooth.

I think it is a sharp looking phone with a very clean, functional design. If I didn’t dislike WinMob so much I’d really be tempted, and with Palm’s tweaks WinMob 6.1 might even be tolerable. But I’d really love to see something like Google’s Android on that kind of hardware. Maybe there is some hope for Palm’s own ‘Palm OS II’ Linux-based OS, it might be nice on a phone like this.

If you like what you see, it’ll set you back $549 for an unlocked model. It apparently hasn’t been picked up by AT&T or T-Mobile, so it isn’t available for less with a contract at this time.

Palm posted a video “featuring three of the Treo Pro’s very proud parents — Stephane Maes (VP of product marketing), Peter Skillman (VP of design), and John Moses (VP of customer relations)” in their blog.