At least that's what a leaked press release (via a news feed) is calling Palm's long-rumored mystery device, set to be introduced later today by company co-founder Jeff Hawkins—first at Walt Mossberg’s D: All Things Digital conference and then in a webcast targeted at media and analysts. (Top picture is of Hawkins with Foleo.)

Apparently, Foleo is a terminal with a large screen and a full-size keyboard that allows users to view and edit e-mail and documents from a smartphone, and synchronize those documents back and forth between the two devices—likely through a wireless Bluetooth connection. A touch of a button keeps a Foleo and smartphone synchronized.

According to the info we gathered, Foleo (due to ship this summer for $499 after an introductory $100 rebate) turns on and off instantly, features fast navigation, is compact, and has battery that lasts up to five hours. It is the first device built by Palm on its new Linux operating system.

There are more applications for the Palm OS, over 25,000, than any other mobile-device platform. And since Palm started shipping Windows Mobile devices early in 2005, it greatly increased the number of developers creating compatible with its smartphones. Palm says it hopes to leverage that developer community to create new applications to extend Foleo's capabilities.

Partners already include DataViz, maker of the Microsoft Office-compatible handheld synchronization software Documents To Go, and mobile browser specialist Opera Software.

Smartphones will ultimately be able to do everything a desktop computer can, according to Hawkins. "However, there are times when people need a large screen and full-size keyboard, he added in a statement. “As smartphones get smaller, this need increases. The Foleo completes the picture creating a mobile-computing system that sets a new standard in."

Palm president and CEO Ed Colligan, like Hawkins when he described Palm's mysterious third-category of product in past interviews, compares the development of Foleo to the innovation that was the original PalmPilot and the Treo, adding that the device is the first in line of such companion solutions.

"It starts today with a focus on wireless email, and we expect the Foleo to grow in features and expand its capabilities as the platform grows,” according to Colligan.

We'll have to wait and see how accurate this information is before making any real judgment about Foleo. However, from what we've gathered so far, it certainly doesn't appear to reach the level of innovation of the PalmPilot for PDAs and Treo for smartphones.

It is difficult to say, but do you think there are many people who would want to carry around yet another gadget, no matter how well it works? For most, the QWERTY thumb-keyboard available in smartphones like the Treo may be enough. And if not, why not just use one of those full-size Bluetooth keyboards that fold down to the size of PDA?

The screen could be the key ingredient for the Foleo, especially in the enterprise, where the device may have the best chance. So how big is the display? It can't be too large and have Foleo still be portable, right?

Or, perhaps, as the name implies, Foleo's display may unfold to become really large?

We'll soon find out.

Update: We just heard from Palm, which confirmed all the details regarding Foleo mentioned above.

Here are some additional details:

Foleo's applications include e-mail, full-screen web browser (from Opera, based on Opera 9), and editors or viewers for common business documents such as Word, Excel, PowerPoint and PDF files. Foleo bundles DataViz's Documents To GO.

It stays synchronized via Bluetooth wireless technology and uses the smartphone's radio or the Foleo's built-in Wi-Fi radio for general Internet connectivity.

Foleo supports both Palm OS and Windows Mobile Treos and works with other Windows Mobile devices with little or no modification, according to Palm. In additon, devices from RIM and Appple as well as smartphones built on the Symbian platform can likely be supported as well.

In addition to a mobile companion, Foleo can work as computer on its own. In additon to Wi-Fi and a full-size keyboard, the 2.5 pound Foleo sports a 10-inch display – nope, the screen isn’t foldable. There's also a USB port, video-out port, headphone jack, and slots for SD and Compact Flash cards for memory expansion.

Palm now has a page to Foleo, check it out to learn more.