For the past couple of years, . cellular carriers have rolled out new wireless data networks, allowing users to browse the Web wherever a cellular signal is available. Mean-while, companies such as T-Mobile USA have opened up thousands of so-called Wi-Fi hotspots, permitting users to access the Web wirelessly at the much faster speeds offered by Wi-Fi. However, users face a trade-off: Cellular networks such as the one offered by T-Mobile USA offer slow dial-up speeds at best; Wi-Fi offers far faster speeds, but the signals generally only travel a short distance.

The new device, the two companies say, will allow users to travel seamlessly between the two networks, maximizing the highest possible speeds. Thus, a user can peck out a Web address on the device while walking down the street and access the Internet using the cellular network.

That same user could then walk into his home or a Starbucks coffee shop and automatically pick up the much faster Wi-Fi signal.

"The whole intent is to bring the best-in-breed" of whatever connection is available, said Scott Ballantyne, vice president of business-service marketing for T-Mobile USA, a unit of Deutsche Telekom AG. The device, called the iPaq 6315, looks like a traditional iPaq--Hewlett-Packard's line of hand-held computers--and comes with an attachable keyboard that can be used with a user's thumbs.

The 6315 will sell for $499. While the Palo Alto, California, company offers wireless-enabled hand-held computers, this is the first H-P product to combine wireless data and voice capabilities. Smartphone sales are expected to rise 50 percent to 100 percent annually. In the ., the 6315 will be available through T-Mobile USA.

H-P is expected to introduce several other wireless hand-held computers, though none will include wireless voice capability.