Palm has unveiled a device which it claims offers smartphone users a more convenient screen size and keyboard. 

The Palm Foleo is essentially a sub-notebook computer with a 10in screen and full-sized keyboard. 

It connects to a Palm or Windows Mobile smartphone through a Bluetooth connection, allowing it to synchronise data and connect to the web.

The device offers five hours of battery life and comes with a built in Wi-Fi radio that allows users to connect directly to the web.

The Foleo runs the Linux operating system, and developers will be able to create additional applications. Slots for SD and Compact Flash allow for memory expansion, and a USB slot will handle peripheral devices. Storage capacity was not disclosed.

Palm's new device is scheduled to ship this summer at a price of $499 (after a $100 rebate).

Palm touted the "smartphone companion" as a more convenient way to read and write large email messages as well as open up attachments.

It also allows users to view and edit documents in Microsoft's Word, Excel and PowerPoint as well as Adobe's PDF.

The Foleo was designed by Jeff Hawkins, a PDA and smartphone pioneer who invented the Treo. He touted the Foleo as a natural extension of the smartphone.

"Smartphones will be the most prevalent personal computers on the planet, ultimately able to do everything that desktop computers can do," Hawkins said in a statement.

"However, there are times when people need a large screen and full-size keyboard. As smartphones get smaller, this need increases. The Foleo completes the picture, creating a mobile computing system that sets a new standard in simplicity."

The Foleo is somewhat similar to Nokia's 770 Internet Tablet. Although much smaller than the Foleo, the 770's 4.1in, 800 x 480 pixel screen lets users surf the web through Wi-Fi or a Bluetooth link-up to a phone's data connection. Both run Linux.

Palm disclosed last month that it was developing a special Linux version designed to run its next-generation Treo phones.  

The company declined to say whether the Foleo will be using this new version of Linux.