NEW YORK (CNN/Money) - Nokia Wednesday introduced a hand-sized portable device for browsing the Web and checking e-mail over wireless Internet connections.

The introduction of the 770 Internet Tablet marks a big push by the world's biggest cell phone maker into a market dominated by Hewlett-Packard, Dell, palmOne and other makers of personal digital assistants. Among cell phone makers, Motorola has released a PDA device.

The tablet is unique for its size -- smaller than most so-called Wi-Fi devices -- and since it runs on Linux, the free operating system. Wireless devices can access the Internet via mobile phone networks or faster Wi-Fi, or Wireless Fidelity, networks.

The 770 is due to ship early in the third quarter, the company said, and will sell for $350.

Like other tablet devices, words are entered using a pen and touch screen. The Nokia's screen is oriented horizontally, like a computer monitor, as opposed to the vertical screens of many other PDAs. The screen is larger than those of most competitors' PDAs, measuring 5.5 by 3.1 inches.

Nokia's tablet includes the Opera web browser, e-mail and an RSS news reader, but can be upgraded. The next software release, due in the first half of 2006, will support Internet phone calls and instant messaging, Nokia said in a statement.

Microsoft introduced a tablet personal computer running a version of its Windows XP operating system in late 2002, but the device sold poorly as corporate tech buyers were skeptical of its workplace potential.

Nokia unveiled its new tablet, which is being aimed mainly at consumers, at the 2005 LinuxWorld Summit in New York. It is the company's first product without a mobile phone component.

Researchers at IDC said that tablet PCs account for less than 0.5 percent of worldwide PC sales.

Nokia's (down $0.09 to $17.03, Research) U.S. shares sank about 2.5 percent.

Nokia recently revamped its struggling N-Gage phone and game player. Read more here.