Wireless-industry types like to talk about "smart phones" as if these souped-up, Internet-capable, multifunction cell phones all have the same IQ. But they don't.

Some, barely brighter than average, offer only basic address-book and calendar programs, plus the ability to run a few add-on programs. But with just a phone keypad, they remain read-only devices; you might check your e-mail on these things, but you wouldn't want to write much of it.

Others go too far in the opposite direction; they're really handheld organizers which have had a speaker and microphone soldered on. They're fine Web browsers but terrible phones.

So far, PalmOne's Treo 600 has done the best job of balancing voice and data use. But the Treo is about to have company; early this fall, T-Mobile will introduce a smart phone with some of the same thoughtful design as the Treo -- and a couple of clever features missing from PalmOne's handheld.

This Sidekick II -- developed by a Palo Alto, Calif., firm with the oh-so-hip name of Danger Inc. -- is on the chunky side as cell phones go, at about 51/8 inches long by 23/8 inches wide by 7/8 inch thick, but it still easily slips into most pockets.

The distinguishing feature of the Sidekick II is its swiveling screen. This color screen stays exposed, allowing you to jump online quickly. But when you need to enter text -- to dial a number or type out a message or Web address -- the screen flips out to reveal the keyboard.

Unlike the two models that T-Mobile has sold since 2002, the Sidekick II adds a built-in digital camera. It's also a good deal thinner than its predecessors, if slightly longer. Its price hasn't been revealed; the older version currently on sale goes for $200 after a $50 rebate.

Despite its odd appearance, the Sidekick II feels natural to talk with -- unless you open the screen, in which case you should use the included hands-free kit. Its keyboard, a bit like a BlackBerry handheld's, is wide enough to allow reasonably comfortable and fast thumb typing. Likewise, the LCD screen, just over 21/2 inches diagonally, is wide enough to make reading Web pages or e-mail practical and mostly pleasant.

The included Web browser rearranges Web pages to eliminate side-to-side scrolling; that can make them unusually long to read, but a speed-scrolling shortcut -- hold down the menu button as you spin the Sidekick II's jog-dial wheel -- eases moving around them. Unfortunately, the "back" command is buried in a submenu and can't be selected with a keyboard command.

E-mail access offered a similar mix of versatility and oversight. Danger's software supports the two major standards, POP and IMAP (the latter means it also can access AOL accounts), but the keyboard shortcut to tell it to check your mail now doesn't have a corresponding menu item, meaning users might miss this command entirely.

This program also appears incapable of deleting a message off your mail server; the spam you discard on this device will show up anew whenever you check your mail from your regular computer.

Instant messaging functions smoothest of all; its AOL Instant Messenger software worked fine, except that it's missing an indicator to show when the other person is typing (as opposed to ignoring you in the hope that you'll stop IMing all the time). A Yahoo Messenger program can be downloaded for free, but MSN's popular service isn't supported as yet.

Like the shots taken with almost every other camera-phone, the Sidekick II's pictures look horrible -- these low-resolution, 640-by-480-pixel shots are blurry, blotchy and often strangely tinted. It doesn't help that the flash isn't engaged automatically. But this camera will suffice for the usual camera-phone tasks of taking snapshots on social occasions and getting spousal authorizations for purchases.

Danger includes a simple but capable suite of contacts, calendar, to-do and memo programs. Other applications can be downloaded from a limited catalogue; most require paying a small fee. This compares badly with the Treo's wealth of third-party software, much of it free.

There's no MP3 playback option; the Sidekick II doesn't have enough internal storage (just 16 megabytes of flash memory) and lacks a memory-card slot.

The lithium-ion battery consistently ran through more than two days of moderate use.

What's remarkable is how Danger has made all of these functions accessible with just a jog-dial switch and four buttons at the corner of the device. In this way, the Sidekick II is like the anti-BlackBerry; its elegantly streamlined design is the polar opposite of the BlackBerry's frequently counterintuitive, inefficient interface.

For the $20 a month that T-Mobile charges for data use -- a sum that covers unlimited Web browsing, e-mail and instant-messaging use on the company's slightly-faster-than-dial-up GPRS network -- you also get an amazingly slick synchronization service. Voice calls, of course, cost extra. All the info on the Sidekick II, from photos to calendar events to e-mail to all your settings, is mirrored on T-Mobile's servers and accessible from any Web-connected computer. There's no need to install any software on your computer, or even to own a computer.

Updates from Web to Sidekick and back happened almost immediately -- I marked a to-do item as done in the Web interface, then saw that item disappear from the Sidekick seconds later. For an extra fee, you'll be able to download Intellisync software to sync up Microsoft Outlook contacts, calendars and task lists.

This is a remarkable piece of work. The one real downside to it is the network it runs on -- T-Mobile is one of the spottier services around, and I encountered gaps in coverage in fairly obvious spots. Fortunately, Danger says its distribution deal with T-Mobile is not exclusive, so AT&T, Cingular and other carriers using the GSM wireless standard can sell their own versions of this later. They should -- customers could use this choice.

Living with technology, or trying to? E-mail Rob Pegoraro at rob@twp.com.

From top left: the Sidekick II's camera lens and flash, its screen and its screen swiveled open to reveal its keyboard.