Developers and accessorizers, take note. A new mobile device is coming, and indications are that it will sell like chocolate hotcakes doused in delicious-sauce. We've got good news for you, too: it's a product by Apple, so it makes a bunch of assumptions about how we'll use it, which in turn means it will beg for additional features and accessories. You, dear developers, can rush in to fill the space.

Here are TMO's projections for the accessories that will be most in demand upon the iPhone's release.

Cases. It goes without saying that this will be the first thing just about every iPhone purchaser will pick up. Apple will probably not ship the iPhone with a case (it doesn't provide one with its iPods), and that widescreen display is begging to get scratched up. Usual suspects like Marware, Belkin, and ShieldZone, to be sure, are already planning their new designs, and they'll be ready to go by June. As with the existing music players and phones, this market is certain to be the most crowded, and most visciously competitive.

High-end headphones with integrated mics. High-end headphones are the best way to get your money's worth out of an iPod. There are currently a wide range of choices, but now the iPod will come as part of the iPhone. Some headphone makers offer phone headsets, but the music experience is not as good as their top-shelf products. To get a piece of the iPhone pie, headphone manufacturers will want to start integrating mics into their products. This is particularly true for in-ear models, which are slower to remove and reinsert than other varieties.

Battery packs. The iPhone may get 5 hours of talk time and 16 hours of music time -- but you have to pick one or the other. iPhone users will learn quickly that they can't watch movies during a cross-country flight and still expect to call for a ride after they land. To fill the gap, we'll see a lot of implementations of external battery packs, and they'll be much more popular than they were for the iPod. After all, charge on your phone is usually more critical than charge on your music player.

Stylus kits. Steve Jobs mused briefly during yesterday's keynote that they could have designed the iPhone around stylus navigation. In typical Jobs fashion, he brushed it aside (his exact phrasing was "yecchh"), but there were people in the audience who were cheering the idea in the moments before Mr. Jobs discarded it. Developers will quickly come up with an iPhone case that house a stylus pen, and hacks that let users navigate the phone's interface. They'll also want to develop notepad apps for doodling and note-taking and make use of Mac OS X's Inkwell technology for SMS input, email composition, and storing notes.

Document readers. Many consumers purchase a smartphone in the hopes that they can travel without their laptop. To make this vision -- which too often goes unrealized -- a reality, developers will have to write applications that read Microsft Office documents, display PDFs, search database files, and give PowerPoint and Keynote presentations.

Clever storage solutions. The most persistent complaint we've seen so far about the iPhone is its moderate storage capacity: 4 or 8GB. Apple clearly chose flash memory because of its cost, power, size, and weight benefits. But if iPhone users really want to bring on the road a bunch of movies, all their music and photos, and a large pile of data, then flash memory just won't cut it. So some of the geekier accessories makers will want to build external hard drives for the iPhone that extend the iPhone's storage capacity (and burn its battery life -- see "Batery Packs," above).

Games. At first glance, iPhone users might not seem too interested in playing games. After all, the market for the PlayStation Portable, broadly speaking, is a generation younger than the market for the BlackBerry. But it seems a safe bet that the iPhone will have greater youth appeal than existing smartphones, and inversely, older smartphone users will take an interest in casual games if they're fun and inexpensive. Just as iPod games are built around the scroll wheel, expect iPhone games to be built around gestures.

Bluetooth/WiFi remote controls. Since the iPhone has built-in wireless connectivity, developers will start looking for clever ways to put them to use. You could use it as a remote control for presentations. (Several developers make this possible using existing bluetooth phones.) Imagine using a zooming remote-desktop style application to wirelessly control your Mac. Or think of the wireless remotes people could create by taking advantage of the iPhone's built-in accelerometer?

WiFi filesharing. Microsoft made a big splash when it argued, during Zune's release, that the music discovery, music sharing, and social networking were the next frontier for the music player. Zune has built in technology that "squirts" music from one Zune to another. The approach has overtones of trying too hard, but it is a cool idea, and developers will look for ways to make it work right on the iPhone. The iPhone's target consumer carries around a lot of data -- music, photos, documents -- that they'll want to share with coworkers and friends. Using Bonjour, an iPhone could connect to its neighbors to allow easy document swapping.

Docking stations. This one isn't all that exciting, but it is true: the iPhone has so many more functions than the iPod that a whole new pile of docks will come along to accomodate it. At one extreme, we can image a dock that adds the keyboard and mouse interface back to the computer inside of the iPhone, and with the help of some additional GUI software, uses the iPhone itself as little more than a CPU, monitor and networking device. That may sound a little silly (or, at least, a difficult development project), but hey -- an iPhone and a dock of this kind would still be cheaper than buying a second computer, so it might be a good option for those that want to take their work home with them, or to a vacation house.

Epilogue
It's important to realize that many of these accessories and applications will require Apple to cooperate with developers -- something it can do very well, when it decides it wants to. There are reasons to be wary, however. The "OS X" that runs the iPhone is not the "Mac OS X" that runs your computer; rather Apple extracted a subset of technologies from the latter to build the former. For that reason, there's no assurance that technologies like Inkwell and Bonjour will be included in the iPhone. Similarly, devices like the "clever storage solutions" described above would require some sophisticated communication with the iPhone's built-in storage, which in turn requires that the relevant Mac OS X technologies make it into the iPhone's OS.

As for application development, including document readers and games, there is so far no indication whether Apple will make this possible. Apple nominally treats its Mac OS developers very well, providing technical assistance, building cutting-edge APIs, and fostering the developer community. But it has largely given iPod developers the cold shoulder -- in no way more dramatically than with iPod games. There are many game developers, big and small, who would love to develop iPod games (and sell them through the iTunes Store), but Apple has released no API for iPod game development.