Last time, we talked about form factors for mobile computers. Most of these, even tablets, are packaged in the familiar "clamshell" design that's been around since the first laptop, the GRiD Systems Compass Computer Model 1101. This design makes a lot of sense for any mobile device, since the folding of the shell does for the computer what it does for the clam -- it protects the delicate insides.
And, indeed, starting with form factors for cell phones, the "flip" clamshell design has proven to be enduring and very popular, especially now that a second LCD display has been added to the outside of many models for caller-ID and other purposes.
There are two more designs worth mentioning here. The first is the "slide," wherein the keypad is concealed and brought into view by sliding apart two segments of the device. The other is the more familiar "candy bar" -- no moving parts, and an exposed screen and keypad. If you choose this option, which is perhaps the most convenient and simplest of all, make sure you learn how to lock the keyboard, especially if you like to put the phone in a pocket. (Ever heard the term "butt dialing"? This can be expensive -- and embarrassing!)
Smartphones, which combine phone and PDA functionality, are most commonly packaged in the PDA form factor, analogous to a wide candy bar design. This design, featuring a larger display than is found on cell phones, is used by essentially all manufacturers, including RIM's BlackBerry line, Motorola's Q, and Samsung's Blackjack. The big question is whether or not the device will have a physical (mechanical) keyboard. If equipped with a mechanical keyboard, the keys will be tiny and suitable for the "two thumb" typing technique only. Soft keyboards, which are displayed on the device's screen, range from those that are usable only with a stylus to those that are larger but still a bit tricky to master.
The biggest question to be addressed when selecting a smartphone, apart from whether the one you want is available from your carrier of choice, is the operating environment supported on the device. I'll cover mobile operating systems in more detail in August, but for now the key choices are BlackBerry, LINUX, Palm OS, Symbian, and Windows Mobile. But Apple's use of its own OS X in the iPhone introduces what I believe will be a key direction in smartphones going forward -- a big OS, coupled with a desktop-class browser (in Apple's case, its own Safari product).
The form-factors mentioned above represent the key choices available today, but innovation in the design space continues at a rapid pace. Consider the HTC Advantage -- perhaps too big to be something one carries everywhere, but that's still a lot of function in a small package. Or the Nokia N800, which isn't a cell phone but can connect to one (for access to the Internet) over Bluetooth. Both of these designs show that a larger screen is possible for those who are more Internet-centric, a growing audience to be sure. Bigger keyboards coupled with bigger screens are also desirable -- have a look, for example, at the groundbreaking Palm Foleo, which is a large screen-keyboard combination, packaged as a clamshell and functioning as an add-on keyboard-display for PDA (and possibly many other) phones.
By no means are we at the end of the road with regard to mobile form factors. And there's probably a product on the market that will meet your needs -- if not, I'd like to hear about it!