Some devices, like Treos and full-size BlackBerrys, opt for the larger size and the keyboard, while others assume you’ll peck out email or Web addresses on a phone keypad.

I’ve been testing a new $295 smart phone from Helio, an upstart company based in Los Angeles, that provides an elegant solution to this design problem. It’s called the Helio Ocean and it can look like either a standard voice phone or a keyboard-equipped email and Web device, depending on which way you open its unusual two-way sliding mechanism.

The Ocean also has some very nice software touches to complement this clever hardware design.

It isn’t as slender as some of its competitors and it has a few downsides, but the Ocean is an innovative, thoughtfully designed smart phone that advances the state of the art. It goes on sale over the next week or so at helio.com and in some retail stores later this month.

Helio not only designed the Ocean, but the phone works on Helio’s own cellphone service, which runs on Sprint’s network at broadband speeds. It lacks Wi-Fi wireless networking.

Plans with unlimited data access range from $65 to $135 a month, depending on the number of voice minutes. For $145 a month, you can get unlimited data and minutes.

When closed, the Ocean is just a roomy screen with some buttons at the top and bottom of a black rectangular body with rounded corners. If you hold it vertically with the screen in portrait mode and slide the screen up, a standard phone keypad is revealed that you can hold to your ear when making calls, just as on a standard voice phone.

If you turn the Ocean horizontally so its screen is in landscape mode and slide it up, a full typing keyboard is revealed that puts you in a comfortable position to compose messages and surf the Web. All the main functions are available in both modes and you can use a headset in either mode.

The software is smart, too. When you physically switch the Ocean from one orientation to the other, the screen display switches between portrait and landscape modes automatically. If you answer the phone while in horizontal landscape mode and you aren’t using a headset, the call automatically is placed in speakerphone mode, because it would be clumsy to hold the Ocean to your ear in that configuration. If you slide the keyboard closed and switch to vertical mode, the call continues and the speakerphone is automatically turned off.

When closed, the Ocean looks a bit stubby but it’s actually slightly smaller in every dimension than a Treo 700 — although it gets larger when the keyboard is exposed.

Voice calls were clear and crisp, and the speakerphone function worked well. It was easy to add numbers to the address book.

From the main screen, you can just start typing anything and the Ocean will either search your address book for the characters you type or initiate a Web search. Web-search results are presented in multiple search engines, including Google and Yahoo, Amazon and Wikipedia, which are arrayed in tabs.

I found the keyboard easy to use and was able to attain good accuracy on it while typing with my thumbs. However, the space between the top row of keys and the bottom edge of the screen is a bit cramped; it took some adjustment to thumb-type well on that row of keys.

The Ocean comes preconfigured for all the major consumer email services, including Yahoo, AOL, Hotmail and Gmail. You can manually add others. The Ocean also supports Microsoft Exchange email.

Unlike a Treo or a Windows Mobile phone, the Ocean doesn’t allow editing of Microsoft Office documents. You can only view them as text files and, in my tests, even that didn’t work. Helio plans new software that would allow the documents to display properly.

Similarly, the Ocean works out of the box with a variety of instant messaging services, including AIM, Yahoo and Windows Live Messenger. It also has multiple media functions. It sports a two-megapixel camera with flash and decent built-in software for displaying photos, and playing music and videos. It also accepts memory cards for expanded storage.

You can simply plug the Ocean into a Windows or Macintosh computer and drag photos, songs and videos onto its internal memory or memory card, if they are in a supported format. But in my tests of this, some photos wouldn’t display properly and none of the album art showed up in my MP3 songs. Helio says the album art will show up if you use synchronization software on Windows, instead of simply dragging the files over.

Despite some limitations, the Helio Ocean is an impressive device that’s fun to use.

• Email me at mossberg@wsj.com. Find all my columns and videos online free at the new All Things Digital Web site, http://walt.allthingsd.com.

I attended the iPhone launch event, and was able to use one for a little while. That’s too brief an encounter to allow me to write a proper review. But I can say that it has the largest and most beautiful screen I’ve ever seen on a cellphone, even though it’s incredibly thin. It felt great in my hand. It has a brilliant new user interface; the handsomest email program and Web browser I’ve ever seen on a phone; a full-blown iPod music and video player built in; and even a cool new voicemail system.

The iPhone has some potential downsides — it doesn’t use a physical keyboard, instead relying on a virtual keyboard on the screen, which may put off heavy email users. It runs on the relatively slow EDGE cellular data network, though that flaw is partly offset by the fact that it can also use speedy Wi-Fi wireless networking. And, with a $499 base price, it’s expensive.

Still, the iPhone made my relatively new Treo 700p seem primitive in many respects when I compared them side by side. And the Apple product isn’t Palm’s only problem.

Palm’s position as the design leader in smart phones has been under assault for months. Major phone makers like Motorola and Nokia have introduced models that have most of the Treo’s capabilities but are thinner, sleeker and lighter — and much less expensive.

The Treo maker is starting to respond, but haltingly. It has brought out a couple of slightly smaller new models, but they’re no match in sleekness or style for competitors like the Motorola Q. They also aren’t as cheap. They do, though, have some advantages in software and functionality that, for some users, will make them preferable.

I’ve been testing the latest skinny contender, the Samsung BlackJack, along with Palm’s newest Treo, the slimmed-down Treo 750. Both of these phones — like the Apple phone — run on the Cingular Wireless network. Both also use Microsoft‘s Windows Mobile software.

The new Treo 750 is slimmed down a bit from the familiar Treo 700 and 650 models. The 750 is also a little shorter, because it does away with the protruding antenna. In addition, it’s a hair thinner and about 16% lighter.

But next to the new Samsung BlackJack, the Treo 750 looks bulky. The BlackJack is a striking, all-black model in the slim tradition of the Motorola Q. It manages to cram a full keyboard, like the Treo’s, into a body that is much sleeker and better looking. The BlackJack is 35% lighter — and 36% smaller overall — than the Treo 750. It has a physically smaller screen, but that screen has a third better resolution than the Treo’s. (Of course, both screens look tiny and grainy compared with the display on the new Apple phone.)

Also, the BlackJack claims 38% better battery life than the Treo, and it runs on a faster data network than the Treo. (Neither phone includes Wi-Fi.) And, to top it all off, the BlackJack is half the price — $199, compared with $399 for the Treo 750.

One of the Treo’s biggest advantages has been its Palm software, which I consider to be better designed for email and phone calls than the Windows Mobile software from Microsoft. But the new 750 model can’t claim that advantage because, while it has Palm hardware, it uses the Microsoft software.

The Treo does have a small software advantage over the BlackJack. It uses a fuller version of Windows Mobile that has more features than the stripped-down version used on the BlackJack and the Motorola Q. And, because it has a touch screen, the Treo is easier to navigate than the BlackJack, which must be controlled with buttons and a scroll wheel on the side.

Also, the Treo’s control pad felt better to me than the BlackJack’s, which was cramped. I kept hitting other buttons on the BlackJack while trying to scroll or select icons.

In my tests, both the Palm and the Samsung sent and received voice calls well. Both also exhibited the clumsiness that is inherent in Windows Mobile — multiple key presses were needed to do simple tasks. Both have basic cameras with resolutions of 1.3 megapixels. (The Apple iPhone’s camera will be two megapixels.)

The BlackJack runs on Cingular’s new broadband data network, called “3G” or HSDPA, while the Treo 750 uses a slower network called UMTS. Oddly, however, in my tests, the Treo was generally as fast or even faster at retrieving Web pages than the BlackJack.

Of these two phones, I prefer the BlackJack. But if you’re in the market for a smart phone and can afford $499, you might want to wait until June for the Apple iPhone. The Apple entry is so full of promise that anyone buying a smart phone in 2007 should at least wait for the full reviews and a chance to try it out.

Email me at mossberg@wsj.com.

The slender Motorola Q, despite software that is markedly inferior to that of the Treo 700p, is wooing some users because it is much slimmer and now can be had for just $99, versus $299 for the Treo. The Nokia E62 is about the size of the Q and also costs just $99 these days. The tiny BlackBerry Pearl is just $199. And Samsung has introduced the skinny BlackJack for $199, too.

So, this month, Palm is striking back with a lighter, thinner, cheaper model of its own, the Treo 680, which is being offered by Cingular Wireless at $199.

Meanwhile, T-Mobile has introduced a new slim, light competitor called the Dash. It has built-in Wi-Fi wireless networking to supplement the slower cellphone data network. And it costs just $149.

I’ve been testing the new Treo and the Dash. Both are OK, but neither is as good as it could be. The new Treo still has great software, but it makes some compromises and still fails to match the new competitors in slimness, lightness or price. The Dash has very nice hardware, but is hampered by lousy software.

The Treo 680 is shorter than the Treo 700, because it doesn’t have the 700′s protruding antenna. It’s about 11% thinner and 14% lighter. But it’s still much larger than the new class of Q-type competitors. The Dash is slightly wider than the new Treo and about the same length. But it’s much thinner and lighter. The Dash feels great in your hand because it has rubberized paint.

This new Treo works just like the 700p. It uses the same Palm operating-system software, which is much easier and faster than the Windows Mobile software used by the Dash and the Q. As I have noted in the past, simple operations like deleting an email or displaying your calendar are usually one-click processes on the Palm OS devices, while they often take two or more clicks, or involve opening menus, on the Windows devices.

Also, the Treo 680, like the costlier 700p, comes with better functionality for handling Microsoft Office documents than the Dash does, even though the latter uses Microsoft software. The 680 has the same large, high-resolution screen as the 700p. By contrast, the screen on the Dash, while bright and vivid, is lower resolution.

But the new 680 is less capable than the 700 series Treos. First, it runs on a much slower cellphone network, called EDGE. This EDGE technology isn’t broadband speed, and is only about one-seventh as fast as the networks from Verizon Wireless and Sprint that the Treo 700 uses. Cingular does have a new network with speeds comparable to Verizon‘s and Sprint’s, but the Treo 680 can’t take advantage of it.

Second, the Treo 680 is a big step backward in terms of its camera. The camera’s resolution is only about a third of a megapixel, while the camera on the Treo 700 — and the Dash — is 1.3 megapixels. Finally, the stylus on the Treo 680 is cheap and just plain awful. It actually bends when you use it.

The Dash is also stuck on the slow EDGE network technology because that’s the best data network T-Mobile currently offers. It makes up for it with built-in Wi-Fi, which is much faster than EDGE, and potentially much faster than the Verizon and Sprint cellphone data networks.

In my tests, I was able to use the Dash for email and Web browsing via Wi-Fi in my office, my home and a couple of coffee shops. The Wi-Fi setup and connection process was fairly easy, and T-Mobile has added software to the Dash that guides you through setting up access at Wi-Fi hot spots it operates in airports, Starbucks shops and other locations.

In fact, T-Mobile offers a data plan for $30 a month that includes both cellphone Internet service and access to its Wi-Fi hot spots. This is on top of the cost of a voice plan.

There are some downsides. The Dash doesn’t automatically switch on Wi-Fi. You have to do it manually. And, in my tests, it was much slower using Wi-Fi than a laptop was. For instance, in my home, on my very fast Wi-Fi connection, the Dash got just under one megabit per second, while a Mac laptop inches away got over 14 mbps. On a slower network in my office, the Dash got around half a megabit per second, while a computer inches away got 1.3 mbps.

I also found the keyboard on the Dash to be more cramped and harder to use than the one on the Treo. And the touch strip it uses to control volume didn’t work well.

If you have always wanted a Treo, but couldn’t handle the price tag, the 680 may be for you. Just be prepared for its slower speed and inferior camera. If you yearn for Wi-Fi in a slender smart phone, and can put up with a clumsy software interface, go with the Dash.

• Email me at mossberg@wsj.com.