Over the last several months, I've noticed what may be the start of a trend. Several universities are now giving an iPhone or iPod touch to all incoming freshmen. Similarly, a growing number of families are apparently using an iPod touch as a "second Mac" in their home — for quick and portable access to email and the Web. In other words, the trend is to turn to an iPhone or an iPod touch for what, in years past, would have required a laptop computer.

As I reflected on my use of the iPhone, I realized that I am already around 50% on the way to making this substitution. More and more, I pick up my iPhone in preference to any Mac, even when my laptop or desktop machines are just a few feet away. I prefer the iPhone to a Mac for looking up movie times, getting directions, using Twitter, checking the weather, finding a restaurant recommendation and on and on and on.

This led me to think about the next step in this transition: Could a person who doesn't even own a Mac (or PC) use an iPhone as their only computer?

The answer is clearly "No" in many cases. If you need to write a lengthy and complex document in Microsoft Word, you won't be grabbing your iPhone. Neither will you be able to use an iPhone to duplicate the layering, filtering and assorted other complex editing you can do in Photoshop. And that hardly exhausts the list. Still, there are many Mac users that don't use any of these applications. Their computer needs consist entirely (at most) of email, Web browsing, iTunes, iPhoto, occasional word processing and perhaps a few utilities and games. For such users, shifting to an iPhone-only mode could conceivably work. Not today. But soon. All it would take is a few changes and improvements from what exists right now.

Even before such changes arrive, we're off to a good start. For example, you don't need a Mac to do most interactions with the iTunes Store. You can use the iTunes Store and App Store apps right on the iPhone itself. You similarly don't need iTunes to sync your contacts or calendar appointments. With MobileMe, you can directly sync your iPhone data to the MobileMe cloud.

What pieces are still missing?

First, you'd want to be able to create an iPhone Backup file, as you now do in iTunes. You'd similarly want to back up the music and video in your iTunes Library; you wouldn't want them to disappear entirely if you lost your iPhone. For such tasks, an expanded version of MobileMe could fill in the gaps. As broadband speeds increase and online storage gets cheaper, MobileMe and an iPhone could become a complete substitute for just about anything you would otherwise do in iTunes on a Mac.

Once you get beyond iTunes, there will be times when the iPhone's virtual keyboard and touchscreen simply won't cut it. For extended text entries, you'll want a physical keyboard, mouse and a larger screen. In theory, there is no reason why you couldn't add such devices to an iPhone — via the dock connector, Bluetooth or a new hardware option built-in to a future generation iPhone. Of course, you'll also want improved text editing, with features such as cut-and-paste and undo.

You'll want a storage location, beyond the iPhone itself, where you can save your personal documents and other files. MobileMe could again be an answer. Or, for local storage, there could be a way to connect and directly copy files to a flash drive.

This iPhone-connectable flash drive would also work with card readers, so as to allow transfer of photos from a digital camera. There are already iPhone apps that do an impressive job of editing photos. I can easily imagine a future iPhone app matching the feature set of iPhoto.

Yes, doing all of this will probably require an iPhone with significantly more memory and a faster processor than an iPhone 3G. It may take a few years, but it's coming. In some ways, I see this future iPhone as a variation of my hypothetical Mac Micro. There's a danger that, after adding all these peripherals to an iPhone, it winds up too expensive and too clunky to be practical. But I believe this can be managed.

Inevitably, there are some tasks that will not be well suited to this arrangement. Playing CDs or DVDs, for example. Or working with video from a camcorder. That's why the market for Macs and PCs won't be disappearing. An iPhone-only setup will just be another alternative, appropriate for some people but not everyone. Like the MacBook Air.

At this point, you may be thinking that a (currently mythical) Apple netbook would be an even better solution. Perhaps. For me, I prefer an iPhone, a device that I can stick in my pocket when I don't need to be sitting at a desk. No matter what the future holds for the iPhone, I find myself singing the words from West Side Story: "Something's coming...something good."

One more item for my iPhone irritations list: Unwanted Wi-Fi. A few weeks ago, I offered a list of irritations I'd like to see eliminated in the next revision to the iPhone software. With iPhone OS 3.0 on its way, there's just time for me to make one final addition to the list: an ability to turn off Wi-Fi without having to go to the Settings app. Here's why it would be handy:

Suppose you go to your local coffee shop and get on their free Wi-Fi. A few days later, you're in the bookstore that happens to be next to the coffee shop. You take out your iPhone and launch Safari to check out a Web page. But no pages load. Why? Because you automatically re-connected to the coffee shop's Wi-Fi network. However, without entering the shop's current password (which you don't know and don't want to bother getting), you are not free to roam the Internet.

What's the solution? You want to tell the iPhone to get off the Wi-Fi network and use 3G (or EDGE) instead. To do this, you need to quit Safari, go to Settings, and do something such as turning off Wi-Fi. You can then go back to Safari and resume your surfing. One more thing: when you leave the bookstore, you need to remember to go back to settings again and re-enable Wi-Fi. I don't know about you, but this happens to me with annoying frequency.

What's a better solution? Tap the Wi-Fi icon in the status bar while in any app. A message pops up asking if you want to temporarily turn off Wi-Fi. Say OK. Reverse this later, when you are ready to use Wi-Fi again. Unfortunately, this feature doesn't exist in iPhone 2.x. I'm hoping we'll see it in 3.0.