T-Mobile USA is updating its Sidekick cell phones, adding a high-end model and the first Motorola-built entry in the line of quirky gadgets with a screen that swivels to reveal a keyboard.

The new luxury model, the Sidekick LX, has a screen with more than twice the resolution of the previous top-of-the-line model, the Sidekick 3.

Criticism of the low screen resolution has dogged the line, which still has found a home among young people who like to communicate by text message.

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The LX will go on sale online Oct. 17 for $300 with a 2-year contract, T-Mobile USA said Wednesday. The cheapest current Sidekick, the iD, costs $50.

Apart from the improved 3-inch screen, the LX is slimmer than previous models, with a more elegant styling.

It's an attempt to broaden the Sidekick user base among older customers, said Leslie Grandy, vice president of product and systems development at Bellevue, Wash.-based T-Mobile USA.

The LX is also the first Sidekick to allow text messages with attached pictures. Previous models allowed pictures from the built-in cameras to be e-mailed, but Sidekick users prefer text messaging, according to Grandy.

T-Mobile also announced the Sidekick Slide, which breaks away from the Sidekick line in two ways: It's made by Motorola Inc. rather than Sharp Corp., which makes the others; and its screen slides up to reveal the keyboard, rather than swiveling.

The Slide is smaller than the other Sidekicks and is more tightly focused on messaging. For instance, it won't play music until you buy a memory card for it. It will cost $200 with a 2-year contract when it goes on sale Nov. 7.

The Sidekick runs software from Palo Alto, Calif.-based Danger Inc. The first Sidekick was launched by T-Mobile in 2002.

On Tuesday, T-Mobile announced that it was introducing a BlackBerry that can make and receive calls over Wi-Fi in addition to the cellular network.

That substantially reinforces T-Mobile's HotSpotAtHome program, which previously has offered only two low-end phones, neither of them e-mail-oriented devices like the BlackBerry.

With a HotSpotAtHome plan, which costs $20 a month, subscribers can place unlimited calls over Wi-Fi routers at home or on T-Mobile's commercial HotSpot network.

The new BlackBerry Curve costs $250. AT&T launched the same model this spring, but without the ability to place calls over Wi-Fi.