The new aluminum-clad MacBook Air, which I’ve been testing for several days, is billed as the world’s thinnest notebook computer. Its thickest point measures just three-quarters of an inch, which is slimmer than the thinnest point on some other subnotebooks. And it employs some innovative software features, such as fingertip gestures for its touchpad that are similar to those on Apple’s iPhone.

Apple refused to make the most common compromise computer makers employ to create their littlest laptops. Other subnotebooks — a category generally defined as weighing three pounds or less — have screens of just 10 to 12 inches and compressed keyboards. The three-pound MacBook Air, by contrast, features a 13.3-inch display and a full-size keyboard.

It’s impossible to convey in words just how pleasing and surprising this computer feels in the hand. It’s so svelte when closed that it’s a real shock to discover the big screen and keyboard inside.

But there’s a price for this laptop’s daring design: Apple had to give up some features road warriors consider standard in a subnotebook, and certain of these omissions are radical. Chief among them is the lack of a removable battery. So, while the MacBook Air will be a perfect choice for some travelers, I can’t recommend it for all. It really depends on your style of working on the road and what features you value most.

The MacBook Air, which will be available next week, costs $1,800 with an 80-gigabyte hard drive and a generous two gigabytes of memory. A second model, with a faster, cutting-edge, 64-gigabyte, solid-state drive and a slightly speedier processor, costs a whopping $3,100. The $1,800 price for the main model isn’t unusual in subnotebooks, which can easily top $2,000, although some competitors cost less.

In my tests, the MacBook Air’s screen and keyboard were a pleasure to use. The machine felt speedy, even with multiple programs running. And the laptop has the same Leopard operating system, superior built-in software, and paucity of viruses and spyware that I believe generally give the Mac an edge. I was able to install and run Windows XP using the third-party Parallels software.

But then there are those trade-offs. The sealed-in battery means you can’t carry a spare in case you run out of juice, and you have to bring it to a dealer when you need a new one. There’s no built-in DVD drive. The thin case can’t accommodate a larger internal hard disk. And the machine omits many common ports and connectors.

The MacBook Air

There’s no Ethernet jack for wired broadband Internet connections and no dedicated slot for the most common types of external cellphone modems. That means that out of the box, the MacBook Air has only one way to get on the Internet — through its fast, built-in Wi-Fi connection. If you’re out of Wi-Fi range, you’re out of luck, unless you buy an optional, $30 add-on Ethernet connector or a cellphone modem that connects via USB.

In fact, the MacBook Air has only three connectors: a headphone jack, a single USB port and a port for connecting an external monitor.

That single USB port is a problem, because so many peripherals use USB. You can buy a tiny, cheap USB hub that adds three more ports, but that’s yet another item to carry.

The lack of a DVD drive is partly solved by some clever software Apple included that lets you “borrow” the DVD drive on any other Mac or Windows PC on your network, so you can transfer files or install new software from a CD or DVD. This worked fine in my tests, in which I installed several new programs from CDs on remote computers, but it requires disabling third-party firewalls on Windows machines. It also doesn’t work for installing Windows on your Mac, for watching DVDs, or for playing or importing music. For those tasks, you need an external DVD drive. Apple sells one for $99.

In my standard battery test, where I disable all power-saving features, set the screen brightness at maximum, turn on the Wi-Fi and play an endless loop of music, the MacBook Air’s battery lasted 3 hours, 24 minutes. That means you could likely get 4.5 hours in a normal work pattern, almost the five hours Apple claims.

But the MacBook Air has another downside: its screen height. Because of the larger screen, the lid stands higher when opened than on most other subnotebooks. So it isn’t as usable as some competitors when the seat in front of you in coach on a plane is reclined.

If you value thinness, and a large screen and keyboard in a subnotebook, and don’t watch DVDs on planes or require spare batteries, the MacBook Air might be just the ticket. But if you rely on spare batteries, expect the usual array of ports, or like to play DVDs on planes, this isn’t the computer to buy.

• 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.

The most tangible example of this new approach is Dell’s XPS One desktop — an elegant, handsome, cleverly designed one-piece computer. If it didn’t have the Dell logo on it, the XPS One might be mistaken for a product of the PC industry’s design leaders, Apple or Sony.

Like Apple’s iconic iMac, the XPS One looks like it’s simply a sleek, flat-panel monitor. The guts of the computer have been stuffed into the back of the screen.

But this new Dell is no mere iMac clone. It makes its own style statement, even though it shares the same 20-inch widescreen display and a similar Intel dual-core processor with the base-model iMac. Where the iMac is squarish and silver, the XPS One is all black and rectangular, with speakers attached to the sides and a wide glass base. It looks more like a small TV set than a computer and, in fact, comes with a built-in TV tuner.

In my tests, I found the XPS One to be much better designed and equipped than Gateway’s iMac competitor, also called the One. In fact, the Dell XPS One is the first Windows all-in-one desktop I’ve tested that I believe matches or exceeds the iMac in hardware design. That’s no small feat, especially coming from Dell.

Unlike the Apple, for example, the Dell has a built-in slot for camera memory cards. It comes standard with a wireless keyboard and mouse, which cost extra on the iMac. Its screen can be turned off with the touch of a button without turning off the computer itself. Its USB and headphone ports are arrayed conveniently on the side, instead of mainly at the rear, as on the iMac.

And, when you wave your hand in front of the black border to the right of the screen on the XPS One, a set of blue, back-lit touch controls magically appear for controlling the playback of music or video. They go away after a few seconds. The Dell also comes with a free year of 10 gigabytes of online backup.

For my tests, I used the least expensive standard configuration of the XPS One, which can be ordered for $1,499 at dell.com/theonepc. It came with two gigabytes of memory (twice the comparable iMac’s standard amount), a 250 gigabyte hard disk and Wi-Fi wireless networking, unusual in Windows desktops.

The computer performed crisply and well for me. I installed several popular third-party programs that weren’t included, such as Microsoft Office, the Firefox Web browser, Apple’s iTunes and Adobe Reader. All worked fine.

I also successfully tested the built-in TV function, which requires a cumbersome external attachment to work with a cable box. I was able to view and record TV shows, something you can’t do out of the box on an iMac.

I still recommend the iMac over the XPS One for several reasons other than hardware design. First, there’s the software. I believe Apple’s operating system, Leopard, is superior to the new Windows Vista operating system, the only choice on the XPS One. In my tests, a reboot of the XPS One took more than twice as long as a reboot of the iMac.

And I regard Apple’s built-in software, especially the iLife multimedia suite, as superior to the Dell’s built-in software, which includes a group of Adobe multimedia programs that are less well integrated and more complex.

The XPS One, unlike the iMac, also came with a bunch of craplets — trial software like Yahoo Music and come-ons for online services like NetZero.

Second, the iMac, unlike the Dell, is immune to the vast majority of malicious software floating around, so you don’t have to run annoying, memory-hogging security programs. The first time I turned on the beautiful Dell I was met with a warning that I had “multiple security problems,” and was led to install a security suite in a complex and tedious process.

Third, defying popular perception, the iMac costs less than the XPS One. The base, 20-inch iMac costs $1,199 — about $300 less. And even if you double the memory, and add a wireless keyboard and mouse to match the Dell, it’s still $1,399 — $100 less than the base XPS One (though Dell is currently running a sale that wipes out the $100 gap). Even the cheapest iMac has a dedicated video card with its own memory, something the base XPS One lacks.

Plus, while Dell offers only 20-inch screens on the XPS One, Apple has higher-end iMacs with huge 24-inch screens for the same price, or less, than the higher-end Dells.

Still, if you want a stylish Windows Vista machine that runs well and won’t cost a fortune, the XPS One fits the bill, despite its unlikely heritage.

• 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.

At first glance, this should be easy. The iPhone uses the same hardware ports as the iPod, which has attracted thousands of accessories. And the iPhone uses a modified version of Apple’s Macintosh operating system, which runs numerous small programs called “widgets” that would be perfect for the iPhone.

But, in fact, using add-on hardware for the iPhone will, in many cases, require buying new gear, or at least adapters to make the old iPod gear work, because of subtle differences in the way its hardware ports work. And there is no way to load Mac software onto an iPhone — even widgets. So you have to access iPhone-specific software through the phone’s built-in Web browser.

I have been testing some of the very first crop of iPhone add-on hardware and software. Some work well, others not so much. I expect to return to this topic when the add-on market is more mature, but here is an early look.

Most of the first hardware accessories are cases and headsets, for both music and phone calls. I didn’t test any cases, though I liked the look of one from Belkin, called simply the Acrylic Case, because it has a kickstand on the back that makes it easy to watch videos on the iPhone without having to hold it upright. It costs $30.

A good guide to third-party iPhone cases, headsets and other accessories can be found at ilounge.com. Apple’s own limited selection of accessories can be viewed at apple.com/iphone/accessories.

Many headphones for the iPod won’t work on the iPhone, because its headphone jack is deeply recessed and the connectors on even expensive headphones just can’t reach in deep enough. Belkin sells an $11 adapter to solve this problem. I tested it with my expensive Shure iPod headphones and it worked.

The bigger problem is that even the costliest iPod headphones lack a microphone and a call-answering button, so they can’t handle the dual functionality of the iPhone — listening to music and conducting phone calls.

Apple includes such a combo headset with the iPhone. It looks like the standard white iPod earbuds, but includes a tiny controller, embedded in the right earbud cord, that incorporates a microphone and also acts as a button. Push it once and it answers calls or ends them. When playing music, a single push pauses a song and a rapid double push skips to the next song. I found these Apple earbuds worked very well and were much more comfortable than Apple’s old iPod earbuds.

If you want to use your existing third-party earbuds or headphones, Shure will begin selling in August a $40 adapter called the MPA-3c. It not only fits the phone’s recessed jack, but also includes a microphone and control button that works just like Apple’s. I tested it with several iPod earbuds, from Apple and others, and it worked fine, though the mic is very low on the cord and must be clipped higher up on your clothing to work optimally.

Altec Lansing has several iPhone-compatible wired headsets in the works. I tested one, the $90 UHS306, due in August, and liked it a lot. It doesn’t require any adapter and it has a combination microphone/control button mounted high up on one cord, plus a second cord-mounted controller for volume adjustment and muting.

Plantronics also plans several wireless Bluetooth headsets to work with the iPhone. Most existing Bluetooth headsets should also work, but only for phone functions. The iPhone doesn’t currently support playing stereo music through Bluetooth. I tested a new Plantronics Bluetooth headset, the $130 Discovery 665, and it worked well. It is available now. Apple will also be bringing out its own Bluetooth headset for phone calls for $129.

Many accessories, such as car audio kits and home speakers, that worked with the iPod’s bottom connector, will require a simple plastic adapter for the iPhone to fit into them. Apple sells these for $9 for a pack of three.

Other accessories that use the iPod connector won’t work right on the iPhone because they don’t reroute the sound from its speaker, a feature the iPod lacks; or because they aren’t properly shielded against interference from the iPhone’s transmitters. New versions are likely to be rolling out. These will display an Apple-endorsed label that says “Works with iPhone.”

I also tested about a dozen add-on iPhone software programs. Most were either rudimentary, pointless, or worked poorly.

There were two that I liked a lot. One is a Sudoku game, at sudoku.myiphone.pl. The second, at showtimes.optimalconnection.net, lets you look up movie show times in any zip code, and links to the phone’s Google Maps program and to the Fandango ticket-buying site.

Still, the whole system of running programs through the browser is more cumbersome and less satisfying than if you could directly install them on the phone.

You can find a growing list of iPhone software at iphoneapplicationlist.com.

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

In fact, this category is getting so crowded that it’s hard to follow all of the contenders. T-Mobile and Sprint, for example, have just announced very similar smart phones running Microsoft’s latest Windows Mobile software. Both feature horizontal keyboards that slide out from beneath the screen. The T-Mobile Wing costs $299 after various rebates, while the Sprint Mogul, which runs on a faster network, costs $399.

But I’ve been testing two other new smart phones that I find especially interesting. One is the latest attempt by BlackBerry maker Research In Motion to appeal to consumers. The other is a high-resolution camera phone by Nokia, which costs more than even the iPhone.

The new BlackBerry Curve 8300, sold by AT&T, is sort of a cross between the maker’s low-end consumer-oriented Pearl and its larger, more traditional models like the 8800 series. It costs $199 after rebate, with a two-year contract.

Unlike the Pearl, which manages its slender size by sporting only a squished keyboard where two letters must share each key, the Curve has a full, if slightly compressed, keyboard. I found it no problem to use accurately. It does, however, use the Pearl-like trackball instead of the famous BlackBerry side-mounted wheel.

To accommodate the keyboard and a wider screen, the Curve is wider and a bit thicker than the Pearl, and has more of the traditional BlackBerry look. And it’s over 20% heavier. But it’s narrower, shorter and lighter than the 8800, though a bit thicker.

The silver-colored Curve doesn’t boast any technological breakthroughs. It’s mostly an attempt to bring the BlackBerry’s email capabilities to a model that doesn’t compromise the keyboard the way the Pearl did. It has all the traditional BlackBerry features, plus a two-megapixel camera, a slot for a memory card, and the ability to play music and videos.

In my tests, I had no trouble at all sending and receiving email on the Curve, taking or displaying pictures, or playing music. I was able to move over some songs and pictures from my own computer, and they displayed and played as promised. Voice quality was fine, and phone talk time is about four hours — reasonable but not outstanding.

In a welcome move, the Curve has a standard headphone jack, capable of playing music in stereo and handling phone calls. It also includes Bluetooth for wireless headsets and use in cars, but it doesn’t have Wi-Fi wireless networking. It also runs on AT&T’s relatively slow EDGE network instead of the carrier’s faster data network. And the Web browser is mediocre.

The Nokia N95 lacks a full keyboard, physical or virtual and its email is primitive, but that’s not its main purpose. This device is the best combination of a camera and a phone I’ve ever tested, and includes a long list of other media features.

The camera boasts five megapixel resolution, highly unusual for a phone, and it takes marvelous photos. When I transferred my shots to my computer, they were large, sharp and vivid, just as if they’d come from a standard camera. The camera has Carl Zeiss optics, autofocus, multiple flash settings and various scene settings. It also has a burst mode capable of taking six shots in rapid sequence.

But getting such a good camera in a phone will set you back a whopping $749. And you can’t buy it through any phone carrier, only from Nokia’s Web site (nseries.com) or from various electronics stores. You have to buy a phone plan separately.

Nokia’s N95, left, and BlackBerry’s Curve 8300

Like the Curve, the N95 has good voice quality, but runs on the slow EDGE network, though a future version could support faster networks. Unlike the BlackBerry, the current N95 also can use Wi-Fi networks. Battery life is only fair: 3.5 hours of talk time. While Nokia touts the phone’s Web browser, I found it to be unimpressive. But the phone includes GPS mapping, with optional navigation. It also accepts memory cards for storage.

Physically, the N95 is small, but chunky; on one side, it looks like a plum-colored camera. If you slide its screen in one direction, the keypad is revealed. Sliding it the opposite way reveals standard controls for playing music and video clips. I was able to move pictures and songs from my computer, but the songs failed to display album covers when played.

For $749, you could buy the Curve and a very nice digital camera. But the N95 is for photo enthusiasts who want an all-in-one device. The Curve is a more mainstream smart phone that aims for a balance of features at a low price.

• 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.

But there are problems with going cord-free. In the case of cellphone wireless headsets, loud street and crowd noises make it hard to hear. And the wireless iPod headphones have been big, bulky units of unremarkable audio quality.

Now, some wireless earphones address those problems. For cellphones, a new wireless headset called Jawbone promises to filter out all that background noise. For iPods, new wireless earphones called Ety8 promise to bring small size and great sound quality to the wireless category. Both products use Bluetooth wireless technology to transmit audio from the device to the ear.

I’ve been testing these two new products and have found that each lives up to its claims. Both are advances that have real advantages over the more standard cord-free competitors. But each also has some drawbacks that might deter some folks from using them.

The wireless Jawbone is a sleek, futuristic-looking gadget made by a small San Francisco company called Aliph. It will be sold, starting Dec. 21, for $120 by Cingular Wireless. The earphone will work with any Bluetooth cellphone, not just those on Cingular’s network. Aliph will also sell the new Jawbone on its Web site, www.jawbone.com. The Cingular model will be silver colored. Aliph will offer it in red and black, too.

What makes jawbone special is its noise-cancellation feature, called Noise Shield. You can stand in front of a blaring boom box or a weed whacker with a Jawbone, and its technology, derived from military research, will almost entirely obliterate that background noise. You can also hear the other party better.

This effect is achieved through multiple small, built-in microphones, including one that rests against your cheek, detecting the vibration of your voice through the bones in your face. The gadget uses that reading to help identify and cancel all other sound that isn’t your voice.

In my tests, on a Palm Treo from Verizon and a Samsung Blackjack from Cingular, the Jawbone worked well. On a downtown street, it silenced the sound of traffic and crowd noise. In an office, it blocked out loud music only a few inches away. The noise cancellation is far better than on any other cellphone headset I’ve tried. Battery life is up to a decent six hours.

But there are two downsides to the new Jawbone. First, it can’t defeat wind. Even a mild breeze made Jawbone calls noisy. Second, it has some user-interface problems. The same button that turns the Noise Shield on and off also raises and lowers the volume, and the beeps of the two are hard to distinguish. I also found it hard to get a comfortable fit, though the unit comes with multiple behind-the-ear loops and rubber earbuds.

If you’re an iPod lover, the Ety8 wireless earphones may be just the thing to replace those trademark white earbud cords. Unlike other cordless iPod earphones, the Ety8s aren’t large, over-the-ear headphones. They’re light, in-ear earbuds. They’re made by Etymotic Research of Elk Grove Village, Ill., a high-end audio company whose wired earphones are highly praised.

The Ety8 earphones cost $300 from the company’s site, www.etymotic.com. That includes the headphones and a small adapter that plugs into the iPod to give it wireless capability. You can also use the earphones with other devices with wireless capability built in. For that, you can buy earphones without the adapter for $200.

Like some other high-end earphones, from Etymotic and from competitors like Shure, the Ety8s are meant to go deep into the ear, and come with rubber and foam tips for a snug fit.

The Ety8 also has tiny buttons on the right earpiece to wirelessly control the iPod. You can adjust the volume, play or pause music, or skip ahead or back — all without touching the iPod, which can be 20 or 30 feet away.

They work with the current full-size iPods, the previous generation of full-size iPods, and iPod Nano and Mini models. Battery life is six to nine hours. The adapter draws power from the iPod’s battery, so it will also reduce the battery life of the iPod itself.

In my tests, the Ety8 earphones worked great, both on a new full-size iPod and on an older iPod Mini. They produced excellent sound and were comfortable to wear, once I got used to a cloth-wrapped cord that connects the two earpieces and is meant to be draped behind your neck.

The big downside of the Ety8 is this: They are ugly. They are relatively large, black rectangles that look like matchbooks pasted onto your ears. If you can get over that, the Ety8 wireless earphones for the iPod are great.

Email me at mossberg@wsj.com.