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.

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.